There are a few steps you need to take in order to do this. In broad strokes the steps are:
Change Ellen rig into a humanoid
Change all of Ellenâs animations into humanoid animations
Download the character .fbx you want. You can do this for free (even for commercial use) by going to Mixamo. Ensure you change all of your new character files and animations to âhumanoidâ.
To import character textures, youâll also need to download a Collada file (.dae).
Delete Ellenâs body and skeleton files.
At this point, you will need to get your hands into the gameâs code a little bit. There are some tutorials on YouTube that show you how to do this.
Because the tutorials online are a bit outdated youâll likely have your character falling through the ground up to their waist. To fix this attach a new character controller to your character and then change the animations. You can download animations for free from a site like mixamo.