To replace a defaced (old) driving license in Kenya, you will need the following documents:
Application form XI (available here)
The defaced licence
Two passport size photos of the applicant (35mm br 45mm, showing head shoulder and full face without hat)
Photocopy of the ID
Payable fees of Ksh. 875
Payable fees of Kshs. 875/= if the licence has less than 3 months expiry period or Kshs 375/= if the expiry period has more than three months.
Present all the above to a Kenya Revenue Authority (KRA) office near you.