Here's a video on doing it. http://www.everymac.com/systems/apple/ma...
You have two RAM slots. If you have two 1GB sticks you will have to remove one or both to upgrade. They do not have to be paired.
Both memory slots can accept an SDRAM module that meets the following specifications:
Double Data Rate Small Outline Dual Inline Memory Module (DDR SO-DIMM) format
1.25 inch or smaller (3.18 cm)
1 Gigabyte (GB) or 2 Gigabyte (GB)
PC3-8500 DDR3 1066 MHz Type RAM
Officially, Apple only supports 4 GB of RAM in the "Unibody" MacBook models. Initial tests at the time these models shipped from site sponsor Other World Computing and the always excellent BareFeats demonstrated that they were capable of stably supporting 6 GB of RAM with one 2 GB module and one 4 GB module. It was possible to install 8 GB of RAM as well, but the system was not stable and it was not recommended to install 8 GB of RAM.
However, some time after OWC and BareFeats published their findings, other third-parties reported that these models are capable of stably supporting 8 GB of RAM. In detailed follow up testing, OWC was able to confirm that the "Unibody" MacBook models are capable of supporting 8 GB of RAM, but if -- and only if -- they have been upgraded to run Mac OS X 10.6 "Snow Leopard" and have Boot ROM Version MB51.007D.B03. Note that you may be required to manually update the firmware for the update to work properly. Earlier versions of the operating system (OWC tested running Mac OS X 10.6.6) and earlier Boot ROM versions are not supported.