I elected to remove all previous versions of SQL and do a fresh SQL install. Why? Multiple reasons, for me. Not all versions of SQL Server support DNN7 and I wasn't sure if installed versions did. I wasn't sure how to connect to existing SQL instances. I didn't have a management console to create databases. I had no existing portals that used the database (because they would have been killed if I removed the database.)
You may not want to remove your SQL installation!!!!!
1. Start button --> Control Panel --> Programs and Features --> find any programs with SQL in name. (see above for images.)
2. Highlight the program to be removed. Click on the Uninstall/Change button.
3. Repeat for each program with SQL in the name. (There will be multiple programs.)
4. Reboot your computer, then go back to Control Panel and check to see if all SQL programs uninstalled.