You can read or download a manual at http://stevespages.com/pdf/remington_572.pdf or you can go to Remington.com and request one.
Which model??
You contact Remington customer service, and ask for an owner's manual for your rifle. Then read and follow the manual.
take bolt off
slide the spring to the 2nd hole and go from there
Action size.
Ask a gunsmith for help
You need to find a good gunsmith
There is several you tube videos showing the procedure Aug 30, 2012.
http://www.cpdonline.com/692509.pdf Engine Manual
Action size.
marauder.homestead.com
A Remington Model 700 chambered for the 7mm 08 cartridge would be a short action as the cartridge is based on the .308 Win.