If you’ve purchased Turnkey Flyers directly yourself, then yes you change swap out any logo at any time. Switching brokers will not be a problem.
If, on the other hand, your broker purchased your account then the logo may be hard-coded in the flyer templates and cannot be changed.
The way to check is easy; just click on the logo in the flyer template. If a box pops up asking for you to select a new image, then you change it. If not, then it’s locked and you will have to re-purchased the flyer package yourself after you leave your broker.