I'm a dunce in the garden so would appreciate some advice.

Some kind regular posters here correctly identified last year the Stellata I
have here - it's now in fully in leaf and a globe of about 5-6 feet in diameter.
Can it be pruned, when should it be done and to what extent?

I've had the help of a gardener who did some pruning for me last year and I can
only guess he's not much better at this than me since most of the roses are
falling under the weight of the blooms- presumably these should have been cut
back more bravely at the time. Is there anything I can do at this time of the
year to set things to rights or must I wait till flowering is over?

help would be appreciated.