What memory ram should i use, and put them in what channel slot?

Does your computer have a 32 or 64 bit OS?

If it has a 32 bit OS, there is no point in putting 5GB in, as you’ll only be able to use ~3.5GB of it.

Secondly, if you run the RAM in dual channel (1A and 1B, 2A and 2B), your computer will only be able to address 4GB – the extra 1GB on the 2GB DIMM won’t appear.

You could run the RAM in single channel mode, but it would effectively half your RAM bandwidth, giving you a performance hit in games.

Just stick them in in any old order and it should work.

Putting two differnent modules (1Gb and 2Gb) in to a dual channel your likely to spend most of your time looking at the BSOD.

Not in my experience, although this was with good old fashioned DDR400.

This is why DIMMs should always be in matched pairs (or trios for a three-channel Core i3/5/7). And @the100thmonkey is correct in that you won’t see more than ~3.5GB with a 32-bit OS. Generally, slots that are the same color are on the same channel, but since you have mismatched DIMMS, it won’t matter what order you put them in since you’ll run into a bottleneck and may not be able to address all 5GB anyways.

Personally, I would get another DIMM, either a 1GB if you have a 32-bit OS or a 2GB if you have a 64-bit OS. With the former route, it won’t matter, and with the latter route you’d have 6GB. Either way, you would be able to run dual-channel and increase your RAM throughput to what it should be instead of running at half-speed.