You said "when I try to install a purchased version it wont download". That doesn't make any sense. It doesn't matter what's installed on your computer. You should still be able to download the program. I can understand if it won't install, but downloading shouldn't be an issue.

 

Normally I would suggest running a repair or reinstall the program and then uninstall, but since this was a trial version, you won't be able to do that. I think you will need to contact Autodesk and ask them how to remove the trial software from your computer.

 

One other option would be to use System Restore to roll back to a time before you tried to remove the trial software. But, you will need to have set a restore point prior to removal of the program. I'm guessing you probably didn't do that, so this may not be a viable option for you at this point, but it is something to keep in mind. Always set a restore point before you do something like installing or uninstalling a program.