Step 1:
Make new updater the one that you want to update.
Rename it to new_updater.exe
Step 2:
Upload it to your patch server: root/Shaiya/*here*
Do not put it in to root/Shaiya/patch/*here*
Step 3:
Change your current version. The new OS updater version is 20. so change it to 21 should look like this
UpdaterVersion=21
Step 4:
Now click the updater.exe it will update and replace with the new updater automaticaly.
About version of updater.exe you can check it using ResHacker. Hope this helps.