Documents such as the constitution are stored in a Subversion repository on the SRCF. Using a version control system entails a bit of effort, but it benefits us by allowing multiple users to edit documents and track changes (hopefully) without stepping on each others' feet.
In order to access the repository you must have an SRCF account. Sign-up for one at https://www.srcf.ucam.org/signup/.
You must also be a member of the SRCF caving group to modify the repository. Email the webmaster to be given access.
Check out the repository from the SRCF server using your CRSID (the bit before the `@cam' in your cambridge email address):
svn co svn+ssh://YOUR_CRSID_HERE@www.srcf.ucam.org/societies/caving/svn
This will give you a local copy of the files which you can then edit.
Once you are done editing, you can check your modifications back into the repository:
svn ci -m 'Informative log message summarising changes'
For more information, read the Basic usage section of the Subversion book.
Windows users can use TortoiseSVN for a graphical interface.