If you were to fill the pot it's in almost to the top, that is about how deep I would plant it in the new container (thats me though). It's really up to you...and really up to the new container size. 3 gal? 5 gal? 7 gal? but again, how deep you plant it is up to you. You won't hurt anything by planting it too deep or not deep enough. Just know that after you re-pot that you won't see much new growth for at least a week, so don't freak out lol It's just your roots getting used to their new home.
There is a ton of information on this site man. I would advise you to read most of the stickied threads in newbie central and go from there. Once you get a good understanding of what you should be doing, you'll get more comfortable making little decisions like this on your own
Best of luck!!