Amazon has updated its Fire TV set-top-box from the model sold for the majority of 2015, and it adds a fair few changes that make it an even more compelling media streamer than ever before.

For a start, there's 4K video output - its headline feature for sure - so it's definitely something worth considering if you haven't bought one already. However, is it worth upgrading if you already own a Fire TV? Or how about if you don't own an Ultra HD TV, is it still worth upgrading then?

We look at the specifications and features of both the older model and the latest Amazon Fire TV with 4K that is available on now.

READ: Amazon Fire TV 4K review: Ultra HD frills for the masses

The original Fire HD was able to stream and then output 1080p video through its HDMI port, with Dolby Digital Plus surround sound up to 5.1. It could pass-through 7.1 audio too.

The latest box is now capable of outputting video at 2160p (otherwise known as 4k and Ultra HD) at 30 frames per second. It can output 720p or 1080p in 60fps. The audio capabilities are identical.

Another of the big differences between the two boxes comes in the chipsets powering them. The latest device is quite simply more powerful and can process actions much more quickly.

The original Fire TV had a 1.7GHz quad-core Qualcomm Snapdragon 600 processor running the show, with 2GB of RAM and Adreno 320 graphics.

The more recent edition needs beefier specifications to be able to process 4K images effectively, while offering all manner of other overlays and content, including X-Ray - Amazon's live metadata service.

That's why there is now a MediaTek 2GHz quad-core processor running the show (two cores at 2GHz, two at 1.6GHz), plus Power VR GX6250 600MHz graphics. It sticks with the 2GB of RAM, however.

Both the original and latest Fire TV boxes have 8GB of internal storage to download apps and games too (actually, it's slightly less as the system takes up some room). However, the 4K Fire TV also has a microSD card slot that can expand the overall storage by up to a further 128GB.

That means you can download many more apps and games as was possible before.

Another big difference between the boxes is Wi-Fi. The previous box has an 802.11a/b/g/n Wi-Fi chip inside, while the current model ups that to 802.11ac. That not only improves reception over further distances, but also offers greater bandwidth for data transmission. Basically, you should be able to stream 4K content wirelessly, even though it also comes with an Ethernet port for those who would rather hardwire the device.

Both boxes are identical in look, save for the microSD card slot on the rear of the latest model. It is also fractionally lighter, but they were both designed to be hidden from view and not draw the eye, so design is fairly irrelevant.

The remote control for the 4K Fire TV is a little longer than the last one, but performs the same functions - including voice control for search.

Importantly though, it now connects to the box through Wi-Fi rather than Bluetooth, as before, to reduce latency (the time it takes before you pressing a button to something happening on screen).

The same is true with a new optional game controller. The previous one was Bluetooth, which had slight latency issues for fast gaming, but the new model is Wi-Fi and will therefore respond better. It also has new buttons, has been redesigned to feel better in the hand and has a headphone port and voice control button too.

The menu and operating system is largely unchanged from the one Fire TV owners are already used to, except there is now a section for 4K Ultra HD movies - films to rent and buy in the higher resolution format. There are also 4K TV shows, mainly Amazon's own original programming, although Breaking Bad and a few others available too. Amazon's are also available as part of a Prime subscription.

Apart from those, the same games and apps are available on the new model as before, although there is one other new feature; Amazon has brought its instant customer support service Mayday to the platform. Call Amazon (or have someone there call you) and you can relinquish control over your set-top-box while they teach you how to perform certain functions.

There is little doubt that the latest Amazon Fire TV with 4K is a far superior version of the set-top-box, but the biggest factor on whether you should upgrade or not is whether you have a 4K TV or not.

The recent model is more capable of playing and streaming 1080p video too, with faster access through the menus and offering a speedier experience all round, but does that make you want to spend £79.99 upgrading?

We think the only non-4K TV owners that might consider it will be those who want the faster gaming abilities, with lower game controller latency. Even then, there are still not enough triple-A titles to play yet anyway.

If you don't have a Fire TV yet though, even if you have a 4K TV or not, Amazon's latest box is undoubtedly one of the best media streamers out there. Especially for the price.