System Memory Upgrade: Should Brand, Size, and Speed Matters?

I want to upgrade my current system's memory (2×2GB DDR3 1600RAM Sticks) by adding 4GB DDR3 stick or 4 GB DDR3 2000 stick, is that possible? Do I really need to match the size, speed, or brand with my current system? After I bought the memory sticks, do I need to pass through the bios before installing? Please guide me what will be the right thing to do. Thank you so much.
