As above, you can use code-management software. They're just managing files, after all.
But, a cheaper and simpler solution is to just create a read-only directory that everyone has access to, and store your good copy of the documentation there.
Next, you will need a group that is responsible for maintaining the documents. This group will receive requests for enhancements, analyse those requests, and then modify the methodologies appropriately. Finally, they will update the contents ofthe read-only directory. This group is the key role, and it's not a full-time job. In fact, you can even make it a rotating assignment. If you have a dedicated standards/architecture team, then this is their job.
Communication is a very important process. Changes must be communicated to all stakeholders. Major changes (new versions) may require re-training. Keep that in mind.
A revision is a minor change to the version, possibly for clarification of existing content. When the key content changes, though, then you have a new version. For example, changing your modelling processes would qualify as a new version.
If you want to get more information, go to a search site (like Yahoo) and search for the keywords "software configuration management" or "SCM". You should get thousands of links to products and services.
You should also consider some form of quality control - are the standards being following correctly.