You probably misused sudo during an earlier update/branch switch.
Never use sudo on OctoPi unless you need to restart the OctoPrint service or are explicitly instructed to do so.
That means no sudo git ..., no sudo ~/oprint/bin/python ... etc. The only thing your need sudo for usually is sudo service octoprint restart.
If you get a permission error, you broke your file system permissions by using sudo wrongly. Yes, you could just ignore this and use sudo with everything from now on, but that will break things. Instead you need to fix those file system permissions (and in order to do this you do need sudo):
sudo chown -R pi.pi ~/oprint ~/OctoPrint
After that, updating/switching branches and installing plugins should work without permission errors.