Push of current branch master was rejected.
Remote changes need to be merged before pushing.
In this case merge is highly recommended, because there non-pushed merge commits. Rebasing them can lead to problems.
1. Commit all your changes.
2. Open VCS -> Git -> Pull.
3. Remote: click blue Refresh button.
4. Tick master branch. Click Pull. Merge if conflict exists.
3. Open VCS -> Git -> Push -> click Push button.