There is a possibility that it may not be the charging port, but a bad battery. If it is the battery, you have to replace it with a new one. Please use our guide on how to replace the battery:
[guide|36640]
If it is the charging port that is defective, you must follow our guide on how to detach the motherboard:
[guide|37003]
Once you remove the motherboard, you are going to have to remove the solder at the four soldering points that keeps the charging port in contact with the motherboard. With your new charging port, you must solder it using the four soldering points on the motherboard.
If you do not want to solder the charging port off and solder a new one in its place, we recommend buying a whole new motherboard. Luckily, we sell the motherboard on iFixit:
[product|IF283-010-2]