how do i go back to the old layout?

Go to your profile, click on the "Edit Profile" button. Once you've done that, click on the "Settings" tab and if you scroll down the page, you'll see the "Forum Theme" category section. There will be a drop-down menu of themes to choose from. The old layout is under the "Metro Blue" name. Click on the name of the theme you want to pick, then scroll down the page and click "Save Account Settings".