You can still upgrade to Windows 10 for free.  Windows will end support for Windows 7 on January 14, 2020.  See the 'Download' link on this page for Media Creation Tool.   You can save this tool to the computer you're upgrading, or save it on a removable drive to use on a different device. 

The files saved on and the software installed with a Windows 7 or Windows 8 operating system will not necessarily be removed, but third party programs may be uninstalled without notice.  Drivers may also be eliminated, and will have to be updated for Windows 10.   An upgrade from Windows Vista or Windows XP will delete any old files or programs.  

An installation wizard will guide you through the upgrade process

You will be prompted to indicate if you want to keep your personal files and applications. 

I’m performing the upgrade tonight.  It requires several reboots. I’ll let you know if it’s successful. 

You may wish to use a service like Zinstall to perform the ugrade and ensure that none of your files are lost.