If you want to move the information from the Disc ID field to Collection ID, here's what you have to do:
first and most important of all, make a backup of your Database.pediadata file and keep it somewhere safe. The data becomes easy to delete once you start to mess around with SQL commands. Now run Terminal (you'll find it in Applications/Utilities) and enter the command: sqlite3
Then drag your Database.pediadata file straight into the Terminal window (that saves you the step of having to enter the path yourself). That'll start the SQL command line. Now you can enter the actual command:

update zEntry set zdiscID = zcollectionID where zcollectionID is null;

This command will move all the Disc ID information into the Collection ID field but ONLY where the Collection ID field is empty; i.e. it won't overwrite any information already present. If you'd prefer to overwrite the information you already entered into Collection ID, use this command:

update zEntry set zdiscID = zcollectionID;

(Note that field names are always prefixed by z.)

Take a look at these forum threads for some additional information: http://www.bruji.com/forum/viewtopic.php?p=7035
http://www.bruji.com/forum/viewtopic.php?t=1878

You'll also find directions in those threads about what to do if you don't have the latest version of sqlite (3.4.0).