Upgrade to Pro 'trial' from 'free'

I would like to ‘trial’ the Pro version. I’m an existing user of the ‘free’ version. How do I initialize the Pro version in my existing installation to test the Pro features?

You can’t.

You can only evaluate the Pro features the first time you install eM Client on that device, and you will have 30 days to do that. After the 30 days have elapsed, you need to activate a license, and then you can never return to evaluation mode.

Ok, can you please advise then the best procedure for me to install Pro and how I fall back to ‘free’ if I choose not to continue with Pro?

As your initial 30 day evaluation has passed, or you have activated a Free license on that device, you can’t have another evaluation period. Sorry.