I have AT&T DSL service and also their 2Wire 2701HG-B wireless modem. Everything works fine. I would like to replace that modem with one that has the latest wireless security technology. In general, how would I go about doing so?
Check your contract doesn't contain a clause about having to use only equipment supplied by AT&T (sometimes this is for the reason that ISPs do mass firmware updates, often just to simplify support).
I would then check AT&T's user support site and see if they have a help file on setting up popular brands of wireless ADSL router to work with their service. I would choose a model they list.
I would also open the 2Wire's user setup screens via your browser and note down the WAN settings ready to apply these to whatever router you decide to install.
Bear in mind that if you change to a wireless n router, you may need to change the wireless adapter in your computer to take advantage of any performance gain -- indeed it might be wiser to buy an adapter of the same brand as the router to ensure compatibility.