Why can't I update my minecraft?

I been trying to update minecraft to 1.7.4 so I downloaded a new launcher and hit play it went to the mojang screen (the one right when you log into minecraft) and then takes me right back to the same screen and I hit play again. I watched many videos and did what they said but it
Still doesn't work.

Did you download the launched from minecraft.net? If you did, try restarting the launcher, or deleting all the files in your.minecraft folder besides saves, screenshots, mods (if you have any), and the resource pack folder (if you use any), then try again.

If that doesn't work, then go rage-mode.

From the launcher you have to go to edit profile(bottom left) and then in the versions list you can choose what you want to go to. Do not press play first, just open the launcher, and then edit profile. Remember to save changes before opening the minecraft player.