Installing a New Battery in My Phone

I have an old, 2011 or about there, Motorola Atrix HD MB886 phone. I was told by my local AT&T store that the battery cannot be replaced. I found on online and bought it. Now, I need to do some home surgery on my phone and replace the battery. Was I being misled or can this actually be done? I'm very good with my hands (changed my own spark plugs)  and am willing to try. Is there a kit (thing to pry the phone open with) that I should have handy? I was assured that the battery was the exact one for the phone by a reputable seller. Does anyone know of a video that would be helpful? 

The battery life was never good even as a new phone. Now it shuts off after just a few minutes use. Charges up to 100% and shuts off at 70% or more left. Otherwise, I love my Android!!

Thanks for any advice you can give! 

Jeannie