I have 2004 GC with 4.7 engine (4 sensors) and one of the sensor connectors has been fused together from touching the exhaust with one wire exposed to the elements and giving P0136 code.

1.Can anyone enlighten me on the the best way to remove the 1/2 sensor, from top or bottom? Tool required?
2. Can the male connector (wiring harness) be purchased new or do I have to head to the junkyards?

 

You will need a special socket to remove the O2 sensor there is a pigtail attached to it, access from the bottom. I would suggest that you get the sensor from the dealership as the sensors are made by NGK, most aftermarket sensors are Bosch and they tend to lag and burnout sooner.
Here's a pic of the O2 sensor location.