Go to pits [shift-p], press "Garage" [its on the right] and click on either the XRG [the one that looks like a Starion] or the FBM [the ickle Single-Seater]
Without knowing how to physically change cars within LFS an S1 or S2 license would be of no use to the OP. Spamming and telling him to buy a license probably isn't a help either.