I checked your site and it looks you have a lot of experience (both as an athlete and trainer) which always helps to justify any price increase in your rates. There are a couple of ways to do this:
-Grandfather in all of your current clients at the current rate and offer the new price to all the new clients. This way you could avoid losing any of your current clients (although if they like training with you this will not be an issue).
-The second option is to let your current clients know about the increase of your hourly rate (either in-person or an email) and let the chips fall where they may. When I increased my rates a few years back, I sent an email to all of my clients letting them know about the increase, so they knew before hand what the new price was. I didn’t offer any reasons why I decided to do that. If you would like to include any, it’s up to you.
Here are some answers to a similar question to yours posted in the past:
I hope this helps.