In the costumes tab of your sprite, find the blue cat face in the bottom left corner. Click on the "Upload" button that pops up, and navigate to find your new costumes.
Go into your blob's code. Click and drag the chunk of code and hold it over your new sprite. Wait for the new sprite to wiggle, then let go of the code. The code should be copied over.
Right now, both your blob and new character are controlled by the arrow keys, which makes testing it a little weird.
Go ahead and change the controller keys for your new character to the letters A and D so you're not controlling the blob and new character at the same time.
If your character is turning upside down instead, you'll need to change the direction type from "All Around" to "Left/Right." This is in the sprite properties.