Let's say you already got the Tier 1, from extension click the Tier 2, inside the extension, click the arrow or Open Plans. This will open the manage membership page, from there click the Switch button, then it will open the payment form again. Just subscribe, it's not gonna charge any cents to your payment method. But always read first before you proceed.
Then you can repeat the same process with Tier 3.
Once done, make sure to cancel the subscription to avoid any unexpected charge.
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