Subscriptions upgrade using S2 member pro

We are using s2 member pro and paypal . With 4 membership plans at 100, 200, 400,900 we want to allows users to upgrade if they have exhausted the quota at any membership level prior to terminal date.
We are having difficulties particularly when user tries to upgrade membership from our site they are first redirected to PayPal to cancel existing subscription, they are then directed to our site to sign up for a new one which takes them to PayPal again where they sign up for a new subscription.
This back and forth between our site and paypal is inefficient. We would like to ask experts if we are doing something wrong and can we so smarter and more efficiently. Help is highly appreciated . Thanks