Create a better one, and then ask a moderator with jurisdiction over that board to switch the pinned thread. There's no need for any big debate about it: if there's a thread which hasn't been updated in several years, and somebody is asking me to pin a different thread which seems better after a few minutes of skimming, I'm probably just going to do it. (But please try asking other mods first, rather than me.) If somebody ends up having a problem with something-or-other regarding the new thread, then they can make a better thread, and we can at that time have a public debate in Meta about which up-to-date thread is better.
I agree with this The op of this post is right we have so many outdated post on the forum and many of them are as a result of the fact that majority of the creators of these posts are no longer active. Personally I have done an update on one of 1miau's Electrum guide to subside fees. Infact the guide was quite vague because that version of Electrum was way too old.
Anyways saying a thread should be unpinned by a moderator is something I hardly see here to be frank. I have seen new threads pinned but replacement I haven't seen. Personally I think before a thread should be replaced , it should be self moderated to clear spam obviously, and also the creator should be ready to update it from time to time if not it's same as leaving the old thread pinned.
In addition the old thread should also be linked for reference purposes.