You only need to do one of the below, it just depends on which mode you're using.
When in the 'My Team' mode, go to the 'Corporate' tab and then into 'Contracts'. You'll need to buy all of the available upgrades in the 'Driver Perks' section which you can find in the bottom-right of the screen.
When in the 'Driver Career' mode, go to the 'Contracts' tab. You'll need to buy all of the available upgrades in the 'Driver Perks' section which you can find in the bottom-right of the screen.