YouTube does not support .fbr files if that is what you are trying to upload.
However, there are still 2 ways that you can upload to YouTube:
Are you using the option to show the webcam while you are recording? If you are, then the image that you see on screen is recorded as part of your screen and cannot be changed. In that cse, you would have resize the webcam window before recording. However, if you are not showing the webcam whilst recording, it is recorded separately and then embedded on top of your screen recording - when you open the recording in the Player, this allows you to be able to click and drag the image to reposition and resize it.
And just to add, while FlashBack can capture some video games, it was really designed as a more general purpose screen recorder so is not always well suited to capturing them - particularly if they require hardware acceleration to render the image. However, we have been working on a dedicated games recorder named FBX, which has been coded from the ground up specifically to record games. We hope to launch a free beta in the next few weeks so if you would like to take part in the beta to try it out and provide feedback, please let us know.