Lumia Denim was announced at IFA 2014 in September 2014, but its wider roll-out to older Nokia devices has only just started.

Lumia Denim has made its appearance on a number of devices already launched by Microsoft, so if you have a new Lumia, you might already have Denim. It was announced alongside the launch of the Lumia 735 and Lumia 830 and more recently, it was available at launch on the Lumia 535. 

If you have any other Lumia device, you'll want to read on.

Lumia Denim is the latest Windows Phone software, rolled together with what Microsoft previously referred to as "differentiations from Lumia". Last year we'd have said that Denim included the extras that Nokia added, but now that Microsoft has absorbed Nokia's Lumia devices, the position is slightly less clear.

Lumia Denim includes the Windows Phone 8.1 update, as well as these Lumia extras, so although Denim comes from Microsoft, it isn't just the Windows Phone update. 

As we've said, it brings big elements included in the Windows Phone 8.1 update to your device and for many that means that Cortana, the Windows Phone voice assistant lands for the first time.

There are some other tweaks and changes that you'll notice, including home screen folders as a standard feature, better SMS forwarding, as well as being able to set the snooze time on your alarms. 

The Lumia Denim side of the equation adds some additional extras. One of which is Glance Screen, which some devices currently have and some don't, and you'll be able to see more on it, like weather and fitness information, from the new MSN apps. 

You'll also be able to activate Cortana by voice - Hey Cortana - as long as you have the SensorCore technology that it is dependent on.

Then there are a range of tweaks to the camera. The new Lumia Camera brings a range of advantages for some of the top devices, depending on the hardware - Lumia 830, 930, Icon, 1520.

You'll get faster startup, you'll be able to use a long press to jump straight into 4k 24fps video capture, and there will be auto HDR, along with improved algorithms for improved photos, even in low light.

The devices that will get the biggest benefit from Lumia Denim are the Lumia 930, Lumia Icon and Lumia 1520, which have the hardware to support all the new features. Others will likely miss out on some of the camera enhancements.

The Lumia 830, 735 and 535 already have Lumia Denim.

If you're in the UK, then Denim has rolled out for the Lumia 520, 620, 625, 720, 930, 1320 on some networks. Other devices are currently on Cyan, awaiting approval from networks before Denim appears.

The Lumia 1020 and 925 are now getting the Lumia Denim update in the UK. The rollout began on 12 February 2015.

Other devices should be updated in due course.

Fortunately, there's a software list to tell you what the latest software is for your device right here

Lumia Denim will be pushed to your device automatically over the air. If you want to check for the update manually, head into setting > phone update and tap the "check for updates" button.

If you want to know what version of the software you have on your Lumia, head into settings > extras+info and here it says in big lettering the software release you've got (like the lead picture above).

If you have a non-Lumia Windows Phone, you're part of the minority, because in recent times that mostly amounts to the HTC One M8 for Windows. In the case of that device, it's already running Windows Phone 8.1 update, so has many of the core features being added to Lumia devices through the update.