Microsoft has a new Surface device, the Surface Laptop, which comes running Windows 10 S out of the box.

The thing about Windows 10 S is that it is designed to run Windows Store apps only. If you've bought the Surface Laptop, you may want to consider upgrading to Windows 10 Pro. It's a free upgrade after all, as long as you meet the criteria and take advantage of the offer before it expires later this year. With Windows 10 Pro, you get the full Windows 10 experience and aren't limited to specific apps in the app store.

Here's everything you need to know about how to upgrade to Windows 10 Pro from Windows 10 S.

Windows 10 S is described as a fully-functional version of Windows that is designed to run smoothly on all hardware. Microsoft hasn't revealed exactly what the S stands for, but it claimed that its evolved from features that teachers have asked for - hence the education tie-in. Those things include things like faster log-in, better battery life, and, apparently, the ability to only run verified apps.

That's the big catch with Windows 10 S: it's designed to only run verified apps from the Windows Store. You will not be able to download apps online and install them, so this version of Windows is essentially sandboxed. You can learn more about Windows 10 S from our guide here. As for Windows 10 Pro, it's a higher-end version of the Windows 10 OS that can install and run any app.

Windows 10 Pro also comes with more sophisticated features, like the encryption software BitLocker, which is handy for when you're traveling and want to lock down your data. It also offers a remote desktop connection between your machine and a Windows 10 Home PC. Another feature is Client Hyper-V, which lets you create a secure operating environment so you can run different operating systems.

You can learn more about Windows 10 Pro, which is primarily aimed at business-class users, from Microsoft's site. The software retails for $199. Keep in mind all versions of Windows 10 come with Cortana, Microsoft’s virtual assistant, which can make calendar entries, take dictation, open applications and local files, search the web, and give directions -- all based on your voice commands.

If you buy a machine, like the new Surface Laptop, that runs Windows 10 S, you can upgrade to Windows 10 Pro with just a few clicks and an update. This will remove the restriction on app installs - an attractive option for those of you who may need an app that's not verified by Microsoft and therefore isn't accessible otherwise. The upgrade will be free until the end of the year, if you fit certain criteria.

First, you need to have a Windows 10 S computer priced at $799 or above. Or, if you're using Microsoft Intune for Education to manage your device (for instance, schools and accessibility users), you can also upgrade for free. But if you don’t fit into either of those categories, then you must pay Microsoft's $49 upgrade fee (UK price to be confirmed), which is processed through the Windows Store, naturally.

The quickest way to begin the upgrade process is to install - or try to install - an app outside the Windows Store. Once you download it and attempt to install it on a Windows 10 S PC, you’ll be warned that the OS is restricted, but you'll also see the following option: "Still want to install apps from outside the Store?" If you do, click the "see how" link, which will open a new Windows Store page.

You'll then see an offer to switch to Windows 10 Pro. You'll also see a breakdown of the difference between Windows 10 S and Windows 10 Pro. If you don't meet the free-upgrade requirements, you'll be prompted to pay the $49 fee. If you're good to go, you’ll see a free upgrade button, which will essentially let you upgrade your license key to Windows 10 Pro. But keep in mind this is a one-way switch.

In other words, you can’t switch back to Windows 10 S. Now, for whatever reason, if you already own a Windows 10 Pro key, you can manually enter that now to avoid the $49 fee. Otherwise, click the upgrade button to proceed. Windows 10 will remind you to backup all your files, and then it'll start the switch, which takes a couple minutes at most. When it's done, your system will reboot.

At that point, you should be running Windows 10 Pro. A notification will tell you if the upgrade worked. Once you see it, feel free to install regular Windows desktop apps from outside the Windows Store.

Check out Pocket-lint's Surface Laptop review to see what we think of Windows 10 S.