S3422DW, how do you adjust the height?

Hi,

I’ve just bought an S3422DW and I can’t work out how to adjust the height? I’ve gently tried to push it down and it won’t move. I am worried about using any more force in case I break it. I’ve already read the manual and it says it is possible to change the height but it doesn’t say how? Can someone tell me how to do this please?