Fitting some 10mm wheel spacers to the front of my Escort GTi but come across a problem.

I assumed the studs would just knock out, but i appears there is something behind them stopping removal. In the middle of there hub there is a large 32mm bolt which i assume removes the hub assembly?

The picture below shows the studs and the object behind stopping removal.

Can anyone tell me how i go about replacing my wheel studs?

Thanks,
James