It doesn't give me the option of doing so, I currently have a level 50 chimchar/treecko and it just says "Evolution: Not possible now".
You must beat Darkrai,Recruit Manaphy,Then one day Manaphy will come up to you and you will unlock a new area to explore(i believe its called Marie Resort) and when you go out of town the two Ursarings will tell you the spring feels different.Then you can go make you two main Pokemon evolve.
Oh and by the way this question was asked already http://pokemondb.net/pokebase/16260/evolve-pokemon-pokemon-mystery-dungeon-explorers-darkness just make sure to look around next time so you don't get in any trouble
You have to beat the game all the way (beat Darkrai), and then you can evolve.
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