It will evolve on it's own.
Metang will evolve at level 45.
Metang evolves into a Metagross at level 45.
Metang evolves into a Metagross at level 45
Metang will begin to evolve into Metagross once it hits Level 45.
Metang evolves into Metagross at Level 45.
It evolves into metang at level 20 and metang evolves at level 45 into metagross
In Pokémon Conquest, after recruiting Metang which you can only do so by finding Beldum (who is available in the Illusio and Valora Kingdoms) and evolving it you can then evolve Metang according to the level of its defensive stat, Metang will not evolve into Metagross until its defensive stat is at least 111.
Metang evolves FROM Beldum at Level 25 Metang evolves INTO Metagross at Level 45
level 45
level 45
level it up to 45 and it will evolve
At level 45.