Hello, I think that you can just upgrade your membership.
Upgrading to platinum question

I've been on gold for 4 months, and plan to upgrade into platinum. Does this mean with the extra 8 month credit i paid into gold will be deducted from the cost of my new platinum membership and therefore the membership renews 1 year from today? or is it 1 year from the day my gold membership started? thanks ahead of time
Yes, any remaining credit for your current membership will be applied to your upgrade.
I've been on gold for 4 months, and plan to upgrade into platinum. Does this mean with the extra 8 month credit i paid into gold will be deducted from the cost of my new platinum membership and therefore the membership renews 1 year from today? or is it 1 year from the day my gold membership started? thanks ahead of time