You can evolve your pet depending on its type. Evolution is available only when the pet is summoned, and since it transfers Exp., the level might decrease when you evolve a pet with a high level.
The name of the pet will remain, and the items in the pet inventory will be transferred to the owner's inventory.
Which pet do you want to evolve?
Evolve a Wolf into a Great Wolf.
Evolve a Great Wolf into a Fenrir.
Evolve a Baby Buffalo into an Improved Baby Buffalo (for Warriors)
Evolve a Baby Kookaburra into an Improved Baby Kookaburra (for Wizards)
Evolve a Baby Cougar into an Improved Baby Cougar (for Mixed Professions)