Adjustments to the Appointments+ plugin

I am trying to get this adjusted for the client. I need to edit the text that says “click a free day…”. Also the title is very small and need to be increased in size. I would ideally like to have a solid color in the background as it looks weird now. And lastly I want to remove the not possible option. Any help would be greatly appreciated. I am on a deadline so thanks for any quick responses.