Time Machine automatically frees up space when the backup drive is full, and you should never move anything from the backup to the Trash manually, because you will end up with those files in Trash without being able to empty it.
Also you will not be able to move them back to the original place.
files backed up by Time Machine are protected by the operating system and can’t be deleted in a simple way.
if running 10.9.x (Mountain Lion) issue the following command in teminal:
sudo /System/Library/Extensions/TMSafetyNet.kext/Helpers/bypass rm -rfv /fath.to.the.file.or.folder.in.trash
if running the older 10.7.x (Lion) system, then:
sudo /System/Library/Extensions/TMSafetyNet.kext/Contents/MacOS/bypass rm -rfv /fath.to.the.file.or.folder.in.trash