LOL, sorry dude, not to take a stab at you, but if you have such a slim grasp on what lenses do what, then how can you say you've out-grown your camera?
Seriously, Zennon stated the most important factors when he said that:
* if you do want to get a completely new camera system and you only have one lens so far, then this is the time to do it because lenses are not cheap, and they don't work across different brands. If you wanted to use your current 18-55 Pentax lens on a Canon camera, it won't work.
* if it's just a matter of wanting sharper, better quality photos, then maybe just a few new lenses attached to the camera you already own will be more than fine. Honestly, even a good quality 3.2MP point-and-shoot camera is more than sufficient to print decent A3-sized pictures. So getting a few different lenses for the Pentax you own already as your skills, requirements and budget allow will bring a whole new level to your photos.
If you wanted to get something that shoots video too, then fair enough.