Hi there William and welcome
Your computer will still work after this date, it will just stop receiving updates.
But the only way to upgrade is to purchase and upgrade and you would want to upgrade to windows 7.
First you need to run this tool to see if your computer is able to (that it has good enough hardware) to run Windows 7
You run it and it will check your computer to ensure it can run Windows 7. If it cannot, your best to purchase a replacement computer (or just keep using Windows XP)
If it can run Windows 7, then you would purchase the upgrade disk here
Click me to open
you then put this disk into the computer and run the upgrade and it will then upgrade the computer to windows 7.
If you would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.