I have an older Remington 870 (about 1980) that I bought for a defense gun but it has the earlier shell carrier that is not slotted. I want to update it. I know I need the carrier and a couple other parts including the bolt. Can someone tell me what I need to make the conversion and where to get all the parts to perform it? Any and all help would be greatly appreciated.

I have had at least one 870 for 40 years and I think it's unnecessary. Different not an 'upgrade', but to each their own. Remington has them all, and usually so do Brownells, and Cabela's. You will need the Flex-Tab carrier, the slide assembly;
F401023 SLIDE ASSEM 12 GA (SLIDE BLOCK, FLEX TAB STYLE)(REPLACES 92949) $22.66
and a new fore end tube assembly;
F102324 870 FORE END TUBE ASSEM N/S 12 GA (FOR PRE-1984 GUNS INCLUDE SLIDE F401023) $37.08
If you can handle a file you can modify your existing fore end tube rails pretty easily.
The carrier Remington lists;
F102190 870 CARRIER ASSEM 12 GA RH N/S $20.60
doesn't say it's the Flex-Tab, but Midway does say it's the 'new' style. The Flex-Tab carrier has a 'U' shaped cut out in it. I would call and ask.

I would definately consider the flex-tab update to be an upgrade, as it makes the gun more reliable by preventing the action from locking up in the event of a specific malfunction. It's especially desirable for a fighting gun, since that malfunction is usually the result of user error, and the stress and haste of a life-or-death defensive shooting is not conducive to perfect technique.

You will need to buy and install a new-style slide assembly, breech bolt assembly, and carrier assembly to fully update your action. These parts can be ordered directly from Remington, either through their website or their customer service phone line. You can also look for used parts, if you're trying to save money.

Virginian wrote:and a new fore end tube assembly;
F102324 870 FORE END TUBE ASSEM N/S 12 GA (FOR PRE-1984 GUNS INCLUDE SLIDE F401023) $37.08
If you can handle a file you can modify your existing fore end tube rails pretty easily.

A new fore-end tube assembly is not necessary; a new-style slide assembly will drop into a set of old-style action bars and function just fine (on the other hand, an old-style slide assembly can't be used with a new-style fore-end tube assembly, which is why Remington's parts documentation calls for a replacement slide assembly along with a new-style fore-end tube assembly for pre-1984 guns).

Virginian wrote:F102190 870 CARRIER ASSEM 12 GA RH N/S $20.60
doesn't say it's the Flex-Tab, but Midway does say it's the 'new' style. The Flex-Tab carrier has a 'U' shaped cut out in it. I would call and ask.

"N/S" stands for new-style, which for the three parts in question, indicates that they are updated flex-tab parts.