To build rules based upon what the customer already has in their subscription rather than by what they are selecting, the Rule Set 'Event' trigger should be "Page Loaded."

Within the Rule Set, the Rule's IF statement "Always True" should be unchecked. Select "Existing Subscription" from the dropdown list of IF statements. Existing Subscription's only option is Equal To. A dropdown list will appear to select which product from the journey the customer could already have on their existing subscription. If there are multiple, then click "Add Rule", switch the toggle from AND to OR, and add another line of "Existing Subscription Equal To ________." 

Please note: In the current state, "Existing Subscription" IF statements cannot live in the same rule as the other product-related IF statements. They can be used in conjunction if they are in separate rules or separate rule sets. 

There are two THEN options to hide plans, you can either hide individual products or hide whole categories of products. Either option will provide a dropdown of the products or categories from the journey to choose from. They are multi-select so as many products or categories can be chosen to be hidden as necessary.

If the customer already has a monthly product, then you want to hide annual products from the update/renew subscription options.

IF Existing Subscription = Monthly Product A

OR Existing Subscription = Monthly Product B

OR Existing Subscription = Monthly Product C

THEN Hide Products: Annual Product D, Annual Product E, and Annual Product F

(alternatively, THEN Hide Categories: Annual Products)

A new rule would need to be created to do the opposite for existing annual products to hide monthly products. 

If the customer already has products on their subscription equal to a "silver level," then you only want to allow subscription changes of equal or greater levels (silver or gold) but prevent downgrades (bronze.)

IF Existing Subscription = Silver Base Product

THEN Hide Products: Bronze Base Product, Bronze Add On, and Bronze Support 

(alternatively, THEN Hide Categories: Bronze)

This way only the bronze products will be hidden, but all silver and gold products on the journey will still show. 

A new rule would need to be created to do the same to hide bronze and silver products from an existing subscription with gold.