Warewolf is licensed under the Afferro GPL open source licence. So you are free to use the code in any way you choose within the parameters of the license. Basically you can change the code any way you want but you must make those changes available back to the main branch and any sub licencing you do must also be Afferro GPL. Please familiarize yourself with the terms of the license. You can read the GNU Affero General Public License version 3 online at GNU.ORG.
There are several ways to get the source code. See Getting the Code.
We use Git as our repository if you are new to Git, we have compiled some useful information to get you started. See Getting started with Git.