This article will show you how to install SmartTheme v3 while using the OP2 version of SmartTheme. Please note that the opt-in form integration of OP2 SmartTheme will be reset once you switch to SmartTheme V3. Other settings of OP2 SmartTheme will be carried into SmartTheme V3.
Note that all your settings from the version 2 Smart Theme will carry over to the Smart Theme v3, with the exception of opt-in form integrations and settings. Those will need to be setup again in the Smart Theme v3.