Rose of Sharon is super easy to trim- just take some hedge shears while it's dormant (not growing leaves) and trim away. It will grow new branches from the buds closest to the cut end. It is, however, quite a large shrub, which people don't tend to realize, so you'll need to keep trimming it to maintain a certain size.
Your shrub isn't bending from the weight of it's flower bud (speaking of which, what you see there are actually seed pods from last year), it's leaning towards the light and away from the shadow of your house. So, you'll need to either move it and plant it somewhere sunnier after you prune it, or it's just going to continue reaching.
Try searching for "How to prune a Rose Of Sharon" on the web and you'll find plenty of indepth answers.