Submitting a patch to the project
Since ReactOS does not have a definite maintainer for each section of the code, you should mail ros-dev and ask for someone to accept the patch.
Test your patch
Thoroughly check that your change works as intended. Test your changes with the latest code from SVN. Something may have changed in the latest code that either breaks your change or causes your change to break something else. Make sure that ReactOS can still boot and that any applications or systems that may be affected by your change still run properly.
Preparing the patch
Make sure that your patch is against the latest code from SVN. Where you have made changes to an existing source file, you will use diff to obtain a file that contains only the changes that you have made: Make sure you have svn on your system (svn.exe on Windows). If you use Windows and don't have this tool, you can obtain it from http://subversion.tigris.org/ (remember to put the subversion directory in your path). To create the patch:
- cd "top-directory-for-all-changed-files"
- svn diff > mypatch.diff
Zip all new files and diffs to existing files and send them to the person that will commit the changes to SVN or submit the patch to Bugzilla.