You can not rename a named instance. If you rename your computer, then you can change the first part of the name to match the new name of the computer.

E.g.: your current computer name is REVDEV, you instance name is REVDEV\REVDEV

you change you computer name to REVTEST, you can now use sp_dropserver/sp_addserver to change your instance name to REVTEST\REVDEV

In your situation reinstall and reattach the databases is the way to go.