I think you mean rommon image instead bootstrap image, actually there is no need for you to upgrade the bootstrap image only if you are planning to run "no service password recovery" Bootstrap program some of the times references the ROM monitor, I only have seen how to upload a rommon image in IOS EXEC mode by doing the following:
820-2#copy tftp: rommon:
Address or name of remote host []? 223.255.254.253
Source filename []? C820_RM_ALT.srec.122-4r.XM2
Destination filename [C820_RM_ALT.srec.122-4r.XM2]?
Loading C820_RM_ALT.srec.122-4r.XM2 from 223.255.254.253 (via Ethernet0): !
WARNING...
Do not attempt ROMMON upgrades unless you know what you are doing.
Writing to ROMMON must note be interrupted.
Do not reset the router during this operation.
Do what you can to ensure power to the router is not interrupted.
The router will reload after ROMMON upgrade is successfully completed.
Do you want to continue?[confirm]
However you can try out to use the following command and see what happens:
820-2#copy rommon: tftp:
You can also reference the following links:
<http://www.cisco.com/en/US/products/sw/accesssw/ps381/products_release_and_installation_notes09186a00800ab6b2.html#54965>
<http://www.cisco.com/en/US/products/hw/routers/ps380/products_configuration_guide_chapter09186a0080118d19.html>
Hope this helps.
