If these have been maintained in a formal shape and you prefer more natural growth, it's perfectly reasonable to selectvely remove some of the stems to begin to open up the shape. Feel free to remove anything dead, twiggy or weak or even major branches if their absence would help to establish a more basic framework. Sharp pruners, immediately after bloom has finished.

The guidelines when pruning are:

Remove all dead wood.

Open up the plant so that air can flow through the plant.

Remove one branch whenever branches cross.

Prune soon. If you wait much longer you will be removing flower buds.