EP

It is not clear from your post whether you have a copy of the image file backed up somewhere. If you do have a back up copy of the image file, then there are several options available depending on whether the switch is still running normally or whether the switch has attempted to boot and has an error.

If you do not have a back up copy of the image file then you need to down load the image from the software center on the Cisco web site (which requires a login with software download capability).

If you have a back up copy or have loaded a copy from Cisco and the switch is still running normally then you would use TFTP to copy the image into switch flash. If the switch is not running normally then you probably need to use xmodem which is discussed in the link provided by Mahmood.

HTH

Rick