Downgrading to an older version of Minecraft
From MC Public Wiki
- Log in to the vanilla Minecraft launcher.
- Click the "New Profile" on the lower left.
- Name the profile "Minecraft 1.7.5 to play on nerd.nu" (or whatever else you'd like to identify it as being 1.7.5)
- In the "Use version" dropdown, select "release 1.7.5"
- Click the "Save Profile" button on the lower right.
- Click the "Play" button with the new profile selected.