I just found a thing you can download that gives you the ability to go to any version in minecarft no matter how old.
I am in love with this thing and decided i wanted to share it with you.
Here is the link.

This is the video link is in the description.
Once you are on the site click your type of PC then what you want to use (java ex.)
Then click the small download button under it.
Have fun

MultiMC does the same thing.

MagicLauncher is the safest way to switch versions and the reason i say this is because.

It is illegal to share any portion of the .minecraft folder.

MultiMC may or may not be 100% legal im not sure i would need to check into a few things before i say so.

Magic Launcher however allows you to launch multiple versions of minecraft by simply copying them before updating and launching them from another area which is legal because you have not shared anything and they did not give you any files they just make it easier for you to launch old jar files.

Sadly, what Chase said is true. Sharing versions of the .minecraft files (specifically the JAR) is illegal. While this doesn't stop people obviously from doing it, we have to act upon the charter as our influence for decisions.

Honestly, these are just one of those things you kinda keep below the table until an administrator gives the thumbs up. Cool find though never the less!

Now don't go saying I said anything ( major lol ) but if you can get your hands on a classic or indev version of the JAR, it is awesome!

Technically how I see it, you already own a license to the game (your account) and you should be able to switch versions as you please, seeing how you technically bought it. Copyright laws, especially international (Mojang = Sweden, and obviously we're Canadian/US), are messy. This is one of those grey areas because while you technically did buy the game and own your rights to it, thus granting the privilege to modify it, you agreed to a terms of service upon purchasing your MC account which you more or less gotta listen to. (Politics isn't fun)

Like i said the only 100% legal way i know is making a copy of the .JAR file before updating. You do own this file so you have every right to do this as long as you do not give it away or even try to sell it.

mad haxxor bro