My character wont Jump?

I'm following this platformer Tutorial.

youtube.com/watch

I get to this point:

And the character won't jump any higher than this.

But before that point it's fine. I initially went a little further with the tutorial, but is had animation issues and wouldn't jump at all.

It also gets stuck in this above animation after failing to jump, but then after that it will jump, but remains in the jumping Animation.

Could it have anything to do with the size of my animation images and polygon collisions?

Does it jump at all? Try increasing jump strength in behavior properties. Also check the position of Origin image point in all animation frames. Ideally, for Platform object the image point and collision polygon should be the same in all frames/animations.

Changing animations properly in platformer game may be a tricky task, I suggest you check some tutorials, see how other people do this:

scirra.com/tutorials/all

Here is one example: