How to go back to previous Asterisk version after upgrade

I recently upgraded to Asterisk ver 11.21.2 on my lab unit , my question is how do i go back to the previous version prior to the upgrade? I haven’t found to much on this topic and I’m relatively new to Asterisk. I did try the “switch-version” command but it kept my box at 11.21.2

Using vanilla Asterisk you just recompile the older version. But first backup the config and remove the new modules generated by the newest.

Thank you for your response navaismo and i hate to ask you this but could you provide the steps / commands ? Like i said I’m new to Asterisk and i was asked to upgrade and i want to make sure i have a backup plan.