Up in the top right corner of this page see where it says "settings"? click that, then look down the left colum for "Paid Subscriptions" and that should be where you upgrade.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk