You can upgrade or downgrade your version of Minecraft at anytime via the options menu.
- Open the launcher.
- Click the Options button.
- Select the version you wish to install from the drop down menu under Version Settings.
- Click Install.
- Wait for the launcher to let you know the download is finished.
- Click the Close button in the options menu.
- If it isn’t selected, select the version from drop down menu under the nickname text box.
You should now be able to run the version you selected. After the game has successfully launched, the next time you may want to enable Fast Start from the options menu.
This option skips all the pre-start checks when ever you launch the game.