If you want the easy answer - and you do at this point - just save it to 6x4 and leave it alone. MPix will do a very fine job making the print.
A week after you get the prints, take some of your favorites, and inspect them with a critical eye. Do you think they could be printed better? If so, why?
Then post an example photo, tell us what you think was wrong with the print, and we'll help you along and guide you to making it better - IF we think it can be done better.
There are many many big fat books out there, all about Photoshop and color and sharpening and printing and all sorts of stuff. Any one of those topics can take a while to learn, and years to master. You can't learn it all at once.
And the fact is, if you're happy with the prints, then you don't have to do things any differently. You may want to, but you don't have to.