I purchased the upgrade to Pro yesterday and got a confirmation email via Google Play, but the app hasn't upgraded and no instructions were provided.
It is tied into your Google account so you will need to be signed into your account to see it as the Pro version.
If it still isn't activating/ showing as Pro when signed into your Google account then as you purchased from Google Play Store your purchase and licence are registered at Google not at CCleaner, so it's Google that you will need to contact about that.