A common task - merge software changes from trunk with branch and vice versa - is an easy task with IntelliJ IDEA. There are a couple of ways how to do this in IDEA. Recently, I found the easiest way in my opinion. Assume, we would like to merge changes in trunk with branch.
1) Check out the branch as a working copy.
2) Go to the menu "VCS" --> "Intergrate Project".
3) Select the checked out branch project on the left side.
4) On the right side, select branch URL and revision number, where you want to merge to, for the "Source 1".
5) On the right side, select trunk URL (revision HEAD), where you want to merge from, for the "Source 2".
6) Uncheck "Use ancestry" and click the "OK" button.
You're done. Review made changes in the "Changes" view and commit them. Happy merging!