you can search for a free update 7 to 10 but normally only for the home versions.
On Ebay, etc you can buy an upgrade 7 pro to 10 pro. Be sure to look for an upgrade, not a new installation!
If you have software running that doesn't work on win 10 it is possible that your installation will stop halfway or you wan't be able to use that software anymore.
Upon upgrading 7 to 10 you must make sure that the power is not disconnected. Normally it takes several hours depending how fast your laptop/desktop is.
If your hardware is very old, you might consider to buy a new computer. I upgraded 3 laptops and one desktop, the laptops are fine but the desktop is now slow and upgrading all the time.
Hope this helps a bit.
Jo from Belgium