It depends on the model. There's a 100psi version and a 125 psi version.

If you got the 100 psi version with the digital Elektronicon controller, there's no way you can set the pressure higher than 100 psi.

If you have a 125 psi version with the Elektronicon controller, you can simply adjust settings in the menu.

If you got one of those old beasts with analog control, you can try to increase pressure on the pressure switch (inside the compressor). But, it's your own risk. I'm not sure what the exact difference is between the 100 and 125 psi version, or which version you got. Maybe the latter got a bigger motor, I'm not sure.

update: sorry, i read 'GA 11' but I see you have a GA 111 ... those only come with the analog control. To change the pressure, open the side panels and find the pressure switch. You can adjust the pressure there. As said, be careful not to overload the compressor if it's not designed to go that high.

You can see my pressure switch page for more information:

http://www.air-compressor-guide.com/learn/air-compressor-parts/air-compressor-pressure-switch

Good luck!

Cas