Diff between tips of two branches
git diff branch1..branch2

Diff from their common ancestor
git diff branch1...branch2

Diff between two commits
git diff commitA commitB

Rebase onto
git rebase --onto this-branch start-from-here this-branch

Delete a remote branch
git push -d remote-name branch-name

Delete a local branch
git branch -d branch-name

Delete a remote tracking branch
git branch -d -r remote-name/branch-name

Change url of remote
git remote set-url origin new-url