Depending on its type, you may be able to evolve your pet. Evolution is only possible when the pet is summoned. Also, since the process transfers the experience value, evolving a high level pet might actually result in a decrease in the pet's level.
Any items in the pet's inventory will be transferred to the owner's inventory.
Which pet do you want to evolve?
Evolve a Great Wolf into a Great Snow Wolf.
Evolve a Wind Strider into Red Wind Strider.
Evolve a Star Strider into Red Star Strider.
Evolve a Twilight Strider into Red Twilight Strider.
Evolve a Fenrir into Snow Fenrir.