install bfg
brew install bfg
delete the file
cd path-to-your-repo
bfg --delete-files your-big-file.fgb
if it is successful, youll see:
BFG run is complete! When ready, run: git reflog expire --expire=now --all && git gc --prune=now --aggressive
then run:
git reflog expire --expire=now --all && git gc --prune=now --aggressive