How to downgrade a 1.7.9 Minecraft server to 1.7.2?

Go to the minecraft launcher and in the bottom left it says "Edit Profile" click that and towards the middle of the options it says "Use version:" click that, then click release 1.7.2 and save your profile.

Find on the internet because Minecraft.net won't have it. Or use a bukkit server. Any way whether on bukkit or Google searching a download for the Minecraft.jar file. Which of course you switch for your new download and call it Minecraft.jar or whatever the previous one was.