On this post: LINK-to-Post , a member question for “How to update/migrate Plex from x86 to x64 (Windows)” and this post solved with: “There is no x64 server build for Windows, yet. So there is no way to migrate.”
But now, there is a x64 server build for Windows available.
So… How to migrate Plex from x86 to x64 (Windows)?
Thanks in advance!
Has been mentioned many times 
A search brings up most of them.
For example … see replies by OttoKerner
Plex x64 Install - Plex Media Server / Desktops & Laptops - Plex Forum
The x64 installer includes an uninstall of x86 that works well now in my opinion. Maybe there’s still pitfalls if you aren’t really careful tho 
Thank you for your replys. I will try to update in the next month