Sure. In your Account page, where the downloads are, you’ll see a login for each that takes you to the archive of previous releases. http://www.s2member.com/account/
http://www.s2member.com/framework/#!s2_tab_jump=s2-framework-archive
http://www.s2member.com/pro/#!s2_tab_jump=s2-pro-archive
Make sure you have Deactivation Safeguards enabled. [hilite path]Dashboard -› s2Member® -› General Options -› Deactivation Safeguards[/hilite]
Via FTP upload the previous version directories to wp-content/plugins/, but add something to the name so it doesn’t overwrite the current ones. When the uploads finish, add a character to the name of the s2Member directories you already had there, and then remove the extra characters from the new directories you uploaded. That’d help keep the downtime to a minimum.
Before this, it’s advisable to create a backup of your site and database, just in case. If you had a backup from before the upgrade, which is also good to do, then you have the option of going back to that.
I hope that helps.