How do you disassemble a Harrington and Richardson model 176 10 gauge magnum with serial number AY487291 and what is the age of this gun?

The letters AY which proceed your serial number indicate that your shotgun was made in the year 1982 by Harrington and Richardson.The disassemble of your shogun,I am not sure about.You may find a manual on E-bay,gunbroker.com,or at gunshows etc.Good luck in your search.