How would i Change position of a gui on click of a button?

So ive got bar at the bottom of my game and i want it to have a button on each side and when clicked it moves the bar to that side by 20 pixels.....and im sorry if this is a noob question, but im a big noob at LUA :P, how would i go about doing this?

I have this button

function die()
script.Parent.Parent.TestMovePos. --this is where i think im stuck at
end 
script.Parent.MouseButton1Down:connect(die)

idk but i hope its as simple as finishing that line...but im not sure.

If somone could guide me to how to do this that would be awesome :)