On the office page, note the icon before the Level x. The same icon is in the top right of the screen. When you click that, you will see that it is a Development rating, which wil lincrease when you get more races under your belt.
You can not upgrade until you have reached the next level of Development rating. I'm not sure by how much the XP will increase after just one race, but it should be 1 or 2 races, yes.
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