What is 'Upgrade'?
'Upgrade' is the opening (purchasing) of the next higher slot in terms of level and cost price (Levels - 1, 2, 3, ...; Price - twice expensive than the previous slot). The upgrade is performed once when you first open a particular slot. The payment goes to your upstream partner, provided that he already has a platform of this level. There is enough income from each slot, to reinvest in the same slot level and buy the next level slot.
The slots are reinvested automatically whereas you decide whether you want to purchase the next level slot or not.
In some cases, where your downline partner overtakes you, the payment is sent to your upstream partner who has that particular platform activated.
Learn more about 'Overtakes' to know how to avoid them and what to do if any downline partner overtakes/supersedes you.