This one flowers on the previous years wood. You can cut it back quite hard but you will lose the next crop of flowers.
It looks as though it could do with being in a bigger pot too, unless its in the ground already - difficult to make out from the photo. If you cut back half of it in the spring and trim the rest at the same time by taking off the dead flowers down to a lively looking bud you should get some flowers. Then do the other half the following year. You could try cutting the front half in the first year to encourage some flowering branches to come out lower down.

Exactly what Steragram has said!