Hi rodpacker and welcome to Tiki Community!
as far as upgrades are concerned, read the documentation: Upgrade
It works in the same way as from Tiki3 to Tiki4, for instance.
Test it first, and check your attachments, and files in file galleries, etc. And if (and only if) you get some problem with them, in your test upgrade, then wait for some information to come at that page Upgrade about UTF-8 issues and how to solve them. (the only different thing that I know of related to upgrades from Tiki4 to Tiki5 compared to previous upgrades.