what it means is, you have to discard any of the RAM sticks it has, to upgrade or to put more RAM....
it's like this, cosider a scenario, a computer has two 256MB sticks and also it has only 2 slots, so both slots are fillesd with 256MB RAM making a total of 512MB RAM..... and the max. capacity of Motherboard is 4GB, but now u cannot upgrade to 4GB without discarding older 256 MB RAM sticks (because there is no space to put new RAM sticks), that's what "With Discard" means....