I work on a project that has 2 branches, A and B. I typically work on branch A, and merge stuff from branch B. For the merging, I would typically do:
git mer
Another, admittedly pretty brute way is to just re-create the branch:
git fetch remote git branch -f localbranch remote/remotebranch
This throws away the local outdated branch and re-creates one with the same name, so use with care ...