Hello Carpa.

 To get level 35,  enlighten the guardian first

If you have another guardian (same type, same color), go to your stronger guardian, click enlighten, select weaker same type, same color guardian, click  again.  

1 sacrifice will increase the stronger guardian level by 1 (30 -> 31).  So you need to find and sacrifice 5 weaker same type, same color guardians to get to level 35  (30->35).  Then fight warlords to get xp and level up.

Good luck

-KJM.