Hi
1) First type dir usbflash0: to list the usb
2) Then type copy usbflash0:c2960x-universalk9-mz.152-7.E7.bin flash:
3) Then config t. boot system flash:c2960x-universalk9-mz.152-7.E6.bin, exit, write and reload
4) Lastly type show version to check version