My own apk and modifying it question

I have an apk that was created a while back by a developer. I cannot get to the developer and more so I need to find a way to modify it somehow.

I have a list of selections on a drop down list inside the apk and I need to modify the words on a couple of selections on that list.

How do I do this and rebuild into an apk again?

I also need to change the version of the apk in order to upload it back to Google Play with these changes.

How do I do that?

Bill