in the directory .../webwork/pg type
This will get the latest bug fixes. To make sure that you are at the latest stable version (which at this writing is rel-2-4-dev) type
cvs update -r rel-2-4-dev
which should get you all the features that Davide mentions. If you want the very latest version (say to grab a recently added feature or bug fix) use
cvs update -A -d
which updates you to the HEAD version in the CVS and also allows new directories to be created.
Will tell which release version you are currently using.
Because you issue this command in the pg directory only the pg files are updated. Issuing this in /webwork/webwork2 would update the webwork2 files (which one should be a bit more cautious about since it usually involves making some adjustments in global.conf)
Hope this helps.