04 cummins solid front axle. Left side seal is out how do i replace it?

 

Replacing the differential axle seals requires pulling the carrier, which requires pulling the axles, which requires pulling the unit bearings. There are specialty tools that can help with the seal installation...not sure they are required (I believe they are called "spanner tools", but are really seal pullers), but they do help.

You should be able to figure out from that whether its something you want to tackle...