How to Rotation a Gui?

For rotation a GUI you don't really need UDim2.new because you'll get error.

The Rotation take only one number because Its 2D

Here your code fixed:

while true do
    script.Parent.Rotation = script.Parent.Rotation - 45
    wait()
end

if you want it more beautifull you just need to just your number 45 and for this you can create a variable like this:

local rotation = 45

now you can write the rest of your code put you need to change 45 for the name of the variable

local rotation = 45
while true do
    script.Parent.Rotation = script.Parent.Rotation - rotation
    wait()
end

Now lets make it more beautifull, theyre is two way for that the first way, you can change the secondes you want to wait or change the rotation

local rotation = 10
while true do
    script.Parent.Rotation = script.Parent.Rotation - rotation
    wait()
end

there is now really more beautifull than later and if you want it more fast you can use

wait(0)-- faster than wait()

or again

game:GetService("RunService").RenderStepped:wait()-- faster than all

here we go, enjoy !