Wait a minute. You just said you want to make it bigger, but you don't want to change the size. Care to elaborate on what makes you think this is possible?
I do not want to change any sizes, because it is used in another composition
How is this even relevant? Pre-comps can have any size and then be scaled, masked and whatever in the parent comp. The obvious solution is indeed to increase the comp/ layer size. You might want to re-check your AE basics.
I mean, the circle should stay the same size.
When I enlarge the composition in the composition settings nothing happens.
And this is the same for when I make the 'size' of the spectrum smaller.
Found the solution, thanks tough!