I'm not sure you can get rid of the message boxes, but I never boither to send the error reports. You could try uninstalling flash totally and then downloading and installing it again.
From internet explorer try, Tools, Internet Options, and then Settings on the general tab, under the Heading Temporary Internet Files. If you click the Objects button, you will see downloaded things which have been installed. Right click the one you want to remove, and select remove.
I think everything in there is safe to remove.