sony vaio svf1521p2eb ram question

[vauxfan]

i have bought this computer and was after upgrading the ram, the sony website said it has 1 card slot and 4gb card. but when i opened the back to add the 8gb of memory i had just bought there appears to be 2 card slots. the bottom 1 has a 4gb card in it but the top has non? am i supposed to put the 8gb in place of the 4gb card or am i supposed to buy another 4gb and put it in the top slot and leave the 4gb thats already in the laptop still in there? or can i put the 8gb in the top slot and leave the 4gb in the bottom slot?

i was always under the impression though that both slots had to match?

any help as sony say this machine onl has 1 slot but it definately has 2.

[billlake]

i would also like to know this question it is very confusing i wish to add more ram and bring the memory up to 8 ram do i buy  4 ram and put it in the other slot or replace the 4 that is there with a 8 ram . its very confusing has it 1 or 2 memory slots?