Well, some RPGs use a complex web of advancement that involves stat increases, skills, feats, class features, increased spell selection, and other increased abilities. This can happen either by "level" or by spending experience to improve specifics aspects of your character. To a new player, this can be a nightmare. Why make it so complex?
In our game, Sam and I put everything on equal footing - skills, spells, feats, etc. When you adventure for a "season," you gain additional abilities. Characters primarily adventure for three seasons a year. So in this way, time will pass, unlike a lot of RPGs (ever been in that game where you characters go from first to tenth level in a month in-game time? - I have even though it took a year in real time).
So going up a level will be easy. A season passes and you simply check the boxes for your new abilities. Done.