... delete  a sprite?

Click on it, hold your mouse down until a red 'x' appears, then hit the x.

... get back to the top of my sprite list?

If your list is frozen and won't let you get to the top, add a new sprite, then delete it, and Scratch Jr. will let you scroll up and down again!

... edit what a sprite looks like?

Click on the paintbrush next to the sprite in the sprite list.

... shrink a sprite?

Use Purple shrink block. Then set the number to however small you want it to get!

... make all my sprites start going at the same time?

If you start each line of code with a green flag block, they will ALL start moving when you click the green flag!