Please do not spam the forum with every question you come up with.  Start reading the in game Help files (located 3 right from the forum button) and www.larkinorguide.com/help

-RTD

the more you steal, the higher level you get.  similar to the more you fight, the higher level you get.
but i ask you to please try to figure things out in the game for a few days before you start asking simple questions like this taking up forum space.  most things you'll be able to figure out within a few days of playing.  and other resources that are good to answer simple questions are found in the help files in the game, or at www.larkinorguide.com
--jason

i tried for 4 weeks

then you aint been trying hard enough because I managed to lvl up Sunstar several times in one week.

i have been trying to steal for weeks but i can't. 

> i have been trying to steal for weeks but i can't. 

Steal exclusively from the drop down "Try to Steal" in the Dark District, Fighter's District or Mage District until you hit stealing level 200.

Sandy