Hi
You can do a free upgrade to Windows 10 at the moment.
https://www.groovypost.com/howto/upgrade-windows-8-1-to-windows-10/Some things you need to do first.
Make a full copy of your Hard drive. If your computer came with the option to make recovery media then do this as well
Check you have at least 30 gb free on your hard drive. If the drive is an SSD then 50 gb free.
Remove any antivirus or malware scanners this not disable, actually un install them.
Check the hard drive for errors and if it is a mechanical drive do a defrag
Run the Windows 10 upgrade if there is any programs not compatible sort these out.
Then complete the upgrade
Install the windows updates and check all the devices are working.
Then do another backup of the Windows 10.
For the backups you will need a drive with at least 2 times the data size used on you computer so if the data on the computer is 130gb a 500gb or 1 TB will be plenty. Even a drive with existing data will be fine.
A program for doing the backups
https://www.easeus.com/backup-software/tb-free.html