Up the Junction>> The 'update_to_2011.php' file will modify the database to 2.0.11 standards.
So basically backup the database/forum files safely before doing anything.
You are getting rid of the MODs right ?
Then upload fresh 2.0.11 files, overwriting the ones on your server. (except the config.php file, don't upload that)
Then, run the update script. In the 'install' folder is the update_to_2011.php file. Point your browser to ...yoursite.com/.../install/update_to_2011.php , which will run it, then afterwards delete the install folder from your forum folder.
A possible problem I can see arising is any database modifications which your MODs may have required - they *may* conflict with the update script. If possible remove any tables/undo any changes to the database which your MODs may have needed. Which is why you should backup everything first.