It depends on what you need.
If your store needs both roles
Your store can be a Source and a Destination store at the same time, without uninstalling. This is called a Universal Store (beta, Shopify stores only).
In your Syncio app, click Enable Source or Enable Destination and follow the prompts.
Your store will then have both a Destination and a Source plan, billed together.
More details: Universal Store
⚠️ Before you enable a second role
Only enable it if this store needs to share its own products with other stores and also import products from other stores.
A store can't connect to itself, so a second role won't sync your store with itself.
Looking for the Orders or Product Settings add-on? Those are turned on in the Destination store's Syncio app, not by adding a second role.
The second role comes with its own plan, even if it isn't connected to any store.
Enabled it by mistake? Deactivate it: select that store type in the top right, click Settings, click Manage under Account Details, click Deactivate store, then finish in Shopify.
If you want to swap roles with your partner store
If your Source store should become the Destination store and the other way around:
Export a product CSV as a backup.
Use Unsync and Keep on your synced products.
Uninstall Syncio on both stores.
Reinstall Syncio on both stores with the new store types, and connect them.
Run the Bulk Mapper in the new Destination store to reconnect your inventory.
The Bulk Mapper works as long as each product has unique SKUs that match on both stores. More details: How can I swap the store type?