The IIsi uses 4 30-Pin SIMMs (Installed in pairs of 2) for a maximum ram capacity of 65MB. It has 1MB soldered to the logic board as well.
Start with this SIMM. Push these 2 metal tabs outward, then push the ram forward. It can then be lifted out. You have to remove the SIMMs in order, starting with the one you just removed. You can then work your way through all of them.