To change color you just start knitting and then weave in the ends later. If you're using two colors and changing that often you can carry them up the side, but make sure you wrap the yarn so they are held against the side. Always bring the new yarn under (I think) the old color. It can show a little when you do that so it's up to you.
When asking questions ALWAYS post the name and a link for the pattern if you have it.