Step 1: Identify the Bloat
Look for code that's been abandoned in the depths of the codebase, or features that haven't been used since the Clinton administration.
Step 2: Quantify the Bloat
Run some find and sed commands to get a handle on just how much junk you're dealing with.
Step 3: Rip it Out
Use a git checkout to revert the changes, or better yet, regex magic to surgically remove the offending code.
Step 4: Justify the Bloat
Write a 10-page memo explaining why this code was necessary, and how removing it will totally break everything.
Step 5: Repeat as Necessary
Repeat steps 1-4 until the codebase is free of bloat and your team is free to roam.