see below links and download the SRT6 Service Manual.
Seems hardest part is
Remove the rear knuckle (1). (Refer to 2 - SUSPENSION/
REAR/KNUCKLE - REMOVAL)
Then half shaft can be pried from the diff ( it is held in by an expandable snap ring )
says you'll need special tool 9223 Drift to install the new seal, but looks pretty simple to rig something up to ensure the new seal goes in straight.