1998 Dodge Neon How to remove and replace the ECM OR PCM?

Electrical problem
1998 Dodge Neon 4 cyl Front Wheel Drive Manual

Hi guys, I recently dicovered that I need a new ECM or PCU (if theres a difference?) On my car. I just replaced the alternator and Battery and still not getting a charge to the Battery. I was advised by the mechanic to replace the ECM/PCM, where as im a student with limited funds, I was looking to do this myself. Also does it matter if the part comes from a automatic or manual if your car is a manual but they are the same car and year?
Thanks, Jeff