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.