There is information on the websites of UPS, FedEx, DHL, aned USPS.
If this is a used computer, be sure to document on the paperwork that goes into the little envelope Kenya requires. Otherwise, you will pay import duties that can be high.
The USPS route is better for single items in many countries, as they bypass the Customs route, but in some countries, it is much more risky.
As a business who ships to Kenya, I can tell you this can be a difficult task. Better to send them money to buy one there.
Do a Gurgle search for "Shipping to Kenya" where you will find an amazing amount of information. Also examin the USPS site thoroughly.
One thing for certain, use only a mainstream shipper, or it can take six months to find out where it went.