You'll have to do this in Flash Builder. Here's a forum thread discussing the issue of changing the loading bar:
The best response is from lui_38 about half-way down the page.
However, I don't recommend completely eliminating the loading bar - your users might wonder why nothing is happening and percieve your site to be unresponsive.
Hi thanks Acath
When I follow the instructions I get errors. Also you said you posted instruction but there is no link on the thread discussing the loading bar.
I think the instructions I was referring to is this:
What problems are you having specifically? I should have mentioned that you might have to do some coding and snooping around - unfortunately we haven't figured out how to make this push-button simple yet.