Lol, what are you reading that tells you to format code that way?
You would need to have something like %client.killsThisLevel to track how many kills the client has had since he last leveled up. You'd want to initialize that variable to 0 when the client enters the game (unless of course you're wanting persistence of levels, but that's something else). Then you would have %client.killLevel which would start at 0 or 1. %client.killLevel would be increased each time the client's %client.killsThisRound meets the number of kills required to level, and then %client.killsThisLevel would be reset to 0.
