1. First download your forge version.
http://files.minecraftforge.net/

2. When you download look for installer not src, javadoc, or universal.

3. Open file and choose client and press o.k .

4. Next open you minecraft and press edit profile.

5.Look for use version

6. Scroll down until you find your forge version and click on it and press save profile.

7. Done =D