Hello everyone!
I can't figure out how to change the pets you are using for battling. Any help?

Hi, to change out your party pets, you'd of course have to go here:
https://www.sylestia.com/explore/party/

If you already have all of your party slots filled, and you have no Party Presets(Saved teams) you can select from the scroll-down menu(It's directly under the text "Use Party Presets to quickly load preselected Parties of specific Pets." which is under your party pets, you'd instead look at your party pets.
If you do have presets, and you want to load one, select the preset from the drop-down menu you'd like to load.

Each party pet that's set as a part of your party should have a in the upper right corner. Click the red minus sign on the pets you want to remove from your party, this will remove them.

After that, below the party preset drop-down menu, there should be two other drop-down menus, one of the left. One on the right.
The one on the left is for stables. The one on the right is for the pets.
This is the text right above those menus "Use the following drop down menus search your Stables for the Pets that you wish to add to your Party."

Select the stable for the pet you want to add to your party, then go to the menu on the right and scroll through until you find the pet you want added to your party. Click the pet's name from the menu.
This will bring up an image of the pet, its stats, and the gear it has on.
After that, next to the drop-down menu for your pets, there's a .
Click the green plus icon, it'll add the pet to your party.

After you've set all the pets you want in your party, under the party pet spaces, press the green "Set Party" button. You'll then have a new party set up you can begin battling with.

If you want to save that party setup, press the green "Create Preset" button. You'll have to name the party when the pop-up comes up, then you'll hit the Create Preset button that's in the pop-up.

Thank you so much! I was going crazy trying to figure it out!

You're welcome, I'm glad I could help. ^-^