What's the git equivalent of "svn update -r"?

git checkout HEAD~1

This will move your current HEAD to one revision earlier.

git checkout <sha>

This will move your current HEAD to the given revision. Use git log or gitk to find the revision you’re looking for.

And getting back to latest (equivalent to: svn up), you'll need to update the branch, usually:

git checkout master

This is because the HEAD refers to the version that is being checked out.