2001 Oldsmobile Aurora Replacing battery in Olds

The battery on our 2001 Olds aurora has not been replaced since 2006. In this extreme cold it is dead. We want to replace at home rather than jump it and drive to a shop. We have located two batteries at oreilly's, super start extreme with cca 850 and an acdelco 770 silver which is what is in it now. Is there anything difficult about this replacement? It looks straight forward to us and we have the owner's manual. Oreillys said they wouldn't do the replacement because it takes too long. Perhaps that is just because of the under the back seat location. Another clerk in a different battery store said there were some special wiring issues to be careful of. Venting is also mentioned but all the venting tubing appears to be in good shape. What are we missing here? Any special concerns?