I'd really like to change a pet into one. I even have the seed, but no longer know how to do it. Halp?

You plant it in the Gardens. Water it every day, and when you pick it, the plant attacks your ACTIVE pet to transform it. So be sure to have the pet you want to change active before you pick the fully grown seed! :)

Edit: The Gardens are at Vetal Lake, btw. Red barn in the top right of Veta's map.

Great! I was worried, since you can't just send the seed to the garden anymore. ^^;; Thank you!