To update, you can either download all files, rename the folder to TotemTimers and copy to the addon folder (World of Warcraft_classic_\Interface\AddOns).
If you just want the modified files, you can copy them over your current addon:
SetupTimers.lua
TotemData.lua
TotemTimers.toc (if you want to get rid of the outdated addon message)
I am not the author of this addon, just modified it to get it to work after the patch was released. I will take this down if the original author asks me to.