[U-Boot] Changing USB speed from slow to fast

Hi,

I am working on ARM at91sam9g20ek. I am copying my Kernel image and rootfilesystem (jffs2) from USB to nand memory in UBOOT. Currently copying files from USB to RAM takes more time and I figured out from the code that USB Speed is low (1.5Mb/s). How can I change it to Fast speed in Uboot?

Thanks for help.

Regards, Nikhilesh Dwivedi