From The GPRO Wiki
If you wish to train and improve your driver, this can be achieved once before each race for a set price.
The available training sessions are:
|Public Relations Training||$500,000|
Each training type will change your drivers attributes in different ways - and it may be that the same training will not always affect your drivers statistics in exactly the same way every time - it's up to you to find out which training sessions affect what driver attributes, but they are pretty intuitive. Once armed with this information, you can then decide what would be the best way forward for your specific driver.