how to update Openfire source code

Hi ,

I am a new bee to openfire server as well as open source development.

I got into a new team and my team has already customized openfire source code, as per needed ( version 3.11 ), but now I have to work on some plugins which require a minimum version of 4.0 .

My question is how do I update my already modified code base ( v -3.11) to latest version of openfire(4.0.1), to support plugins.

I understand in normal development, we can pull from git , but I am not sure, how can this be done in my case.

Please help.