Thanks very much! In fact that's pretty much what I did, without bothering to create a new branch. I used the instructions at
http://webwork.maa.org/wiki/Release_notes_for_WeBWorK_2.10#Upgrade_Instructions
I decided that if I stuffed it up then I'd do a complete clean reinstall. But it all worked pretty well. My only glitch was git complaining about "unmerged files", so I followed the instructions here:
http://stackoverflow.com/questions/8044675/pull-is-not-possible-because-you-have-unmerged-files-git-stash-doesnt-work-do
and entered
git fetch origin
git reset --hard origin/master
git pull
which seemed to fix it all up. Anyway, I'm now running 2.10! (Although with only 1GB of RAM it's more like hobbling, rather than running...)
However, I'm about to move to a more powerful VPS. And I'm hoping that 2.10 will have fixed some of the problems I was having last year, especially with unproctored gateway quizzes. However, item 2 in the "Gateway Updates" section of the release notes indicates that this has been addressed.
Many thanks indeed,
Alasdair