Ground level on Victorian cottage, no foundations

[cottage20]

Hi I have just bought a Victorian Cottage and have damp problems that i am trying to solve by directing water away from the wall. Currently the external ground level runs directly to the bottom of the door frame I want to lower this but there are only 3 courses of brick below and no foundations.

Can anyone please advise me of a safe and appropriate level to set the ground, for information there is no PDC either.

Thank you.