Delete large files from a Time Machine Backup
If you are looking to reduce the size of your Time Machine backup, it's quite easy to go through you backups and remove files.
Just enter Time Machine, locate the file you want to delete, right-click on it and choose "Delete All Backups..." But which files do you delete?
You want to get rid of large files, but not those that are important. The best way to do this is to use an application called GrandPerspective. Pierce Wetter has created a modified version of this application specifically for Time Machine backups.
It searches through your backups, and finds large files that have only been backed up once. These will be the files that either constantly change by small amounts or were only on your Mac for a very short time.
It then produces a nice "map" of your backup, so you can easily see which files are taking up the most space. Hold you mouse over one of large boxes, and make a note of the backup date and location, shown at the bottom. Then just enter Time Machine, go to the date, and remove the backup as usual.
If you find that a lot of the files you are removing are in the same location, you might want to exclude that folder from the Time Machine backup. To do this, just go to the Time Machine section of System Preferences, click the Options button and then drag the folder into the list.