You can't upgrade the bootstrap firmware from ROMmon.
As what Paolo have stated, load the IOS and then you can upgrade the ROMmon from there.
When the 870 series was first released there was no option to upgrade ROMMON from IOS (bug
CSCsg59037, fixed in IOS 12.4(11)T1).
It was possible to upgrade the ROMMON via the tftpdnld ROMMON command - this is described at
However, I don't know if this works for the 1841.