How to choose files to upload after merging branches?

Hi!

I'm on PhPStorm with local git - so far I was working on just a master branch. Finally I had to make new branches to test new concepts and still have the basic version for current tasks.
And I know, that I have to commit changes made on some branch to switch back to master and have my changes visible only on their branches. And when I commit, I can send commited files to my server, but since they aren't finished yet, I do not send anything to my production server.

But I'm stuck on this situation: I have some changes, that are ready to merge with master branch and to send to production server.
How do I know, what files should I send to server after merge?

Or: how should I properly merge branches, to have changes committed and files sent to server.

Thanks in advance for any help on this...

P.S. Is there some way, to undo upload of files after commit? How can I roll back commit and have all files back on a changelist?