EmulationStation only shows emulators that have ROMs in their folders with the correct extension. So you just need to copy them over and it should work for SNES and N64. The easiest way for me is to just use the windows file shares that the retropie creates. So just browse the network and drop the roms in one of the snes/n64 folders.

The expected extensions are in /etc/emulationstation/es_systems.cfg:
SNES .smc .sfc .fig .swc .zip
N64 .z64 .n64 .v64 zip

A few other things:
it is sudo apt-get install lxde

it is /etc/network/interfaces