Friday 29 July marks the last day that users can get a free upgrade to the Windows 10 operating system.
Those who do not take advantage of the offer will have to pay for it, with the home edition costing $120 (£91) and the professional edition $200 (£151).
Eligible devices include tablets and PCs running Windows 7 or newer.
Microsoft has been criticised for heavy-handed tactics in promoting the upgrade.
In May, the software giant was accused of a “nasty trick” when it changed the pop-up box encouraging users to upgrade so that clicking to shut it down meant the upgrade was scheduled rather than rejected.
A Californian woman successfully sued the firm after she claimed that an automatic Windows 10 update left her computer unusable.
In June, Microsoft said that is was going to offer “clearer options” for users considering the upgrade.
To date, around 300 million devices worldwide have upgraded to, or are using, Windows 10.
Most experts agree that upgrading should bring benefits to users.
Windows 10 offers access to Cortana, Microsoft’s virtual assistant – the first major operating system to offer this feature.
The virtual assistant can find restaurants and create calendar events and also syncs with the Cortana app on any phone.
The system is designed to look the same on laptops, phones and tablets, and has a new browser called Edge.
Most agree that the operating system is easier to use and a vast improvement on Windows 8, which was heavily criticised.
It has the same tile-based system used by Windows phones – and reintroduces the Start Menu, which was missing from the previous operating system.
The update requires quite a bit of free disc space to install, so some may need to uninstall space-hogging programs.
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Microsoft has published a list of the most common upgrade and installation issues and advice to try to fix the problem.
Annette Jump, an analyst with research firm Gartner, said there were pros and cons to upgrading.
“Consumers can continue to stay current on Windows going forward, as Microsoft is looking to deliver Windows more as a service in future,”
She also listed improved security as a reason to upgrade but warned it may not be worth it for all: “If you have an old PC – older than three years – you will likely have very low specs on the device and will not be able to benefit from many new features.”