Bicycle Mechanics - Help buying a Chain and Cassette

Hi,
I need a new chain and cassette. I have a Giant FCR3w http://www.giant-bicycles.com/en-us/bikes/road/2268/32201/ and here are the chain and cassette specs:

cassette SRAM PG 830 11/28, 8-speed
chain KMC Z72

I have a $100 giftcard to rei.com and only saw the SRAM PG 850 8-Speed Cassette available for purchase with a 11-32 tooth gear range. I also saw the SRAM PG-850 8-Speed Road Cassette with a 12-26 tooth gear range. Can I use either one of these? Can I also buy this : SRAM PC850 Powerlink 8-Speed Chain?

Any advice is greatly appreciated:)

Your rear derailler will handle either cassette without issue and any eight speed chain will work. Read up on properly sizing your new chain if you haven't already. You'll also need a cassette lockring tool, chainwhip, and chain tool to perform the work.

Why do you want to replace the cassette?

The three tools joejack mentioned will set you back about $35. Size the new chain to end up with the same number of links as the old. If you do a lot of hill climbing, you might like the cassette with the 32 teeth; if you ride mostly on level, choose the 12-26. I am making the same upgrades on my FCR3 with 2900 miles. Both the chain and cassette had significant wear. The Sram 850 chain and cassette represent a grade up from the original components, so they should have improved longevity. If you wish to stay with the original gearing, Niagara Cycle Works has the Sram SG-850, 11-28, cassette for $22.

Size the new chain to end up with the same number of links as the old.

Not if one changes gearing. Measure anew.

DMF is right, if you select a cassette with something other than the original 28 tooth largest sprocket, you'll need to resize the chain. Sheldon Brown writes, "The best technique for setting chain length is to thread the chain onto the large/large combination, without running it through the rear derailer. Mesh the two ends on to the large chainwheel so that they could be connected (outer link meets inner link), then make the chain one complete link (one inch) longer than that. In almost all cases, this will give the optimum length."

Not if one changes gearing. Measure anew.

You should measure new anyways. You have no idea if the previous chain was cut to the proper length to begin with. Some idiot could've done it.

I'm upgrading b/c like member flanso I have significant wear on my chain and cassette plus I am upgrading my wheelsets