Hi Mathew,
What I usually do is go to my 'packages' directory of my instance and run this:
cvs -d:pserver:anonymous@cvs.openacs.org:/cvsroot checkout -r oacs-5-4 acs-developer-support
Then, go to http://yourinstance/acs-admin/apm > click on 'install packages' > select developer support > install and after the whole process, bounce your instance.
http://openacs.org/doc/openacs-5-1/using-cvs-with-openacs.html
Hope that helps