I have a USB flash-drive with some bootable iso's on it and i need a way to make them smaller they must keep the iso file extension and they must be bootable just like they were before. Does any one know how i could do this. Thanks in advance.
Most ISO tools let you "compress" an ISO file, such as described here for MagicISO. I'm not sure what that does exactly, but you could try that.
Bottom line: bootable ISO images have very limited options in terms of compression.