You can see the contents of sd-ext.Go while running a android rom with a root explorer in folder NativeSD and you will see there the folders of the roms that you have installed.You can delete any rom that you dont want,but it will take a lot of time to do it.
A more easy way is to boot in 4ext recovery and flash the script of the rom you want to delete from gtbluesky http://forum.xda-developers.com/show...&postcount=428
i tried it with paranoid and it worked perfect for deleting PA folder from sd-ext.It left PA folder in sdcard/NativeSD folder,so i deleted this manually.
Also even if you are in wm,you can take a full backup of your roms by using in 4ext recovery the advanced backup--->sd-ext option.This will make a backup of your sd-ext contents in sdcard/clockworkmod/advanced/sd-ext folder.
Then you can enlarge your ext partition and go to advanced restore--->sd-ext to restore your contents