While I don’t know how to update existing sites to MediaWiki 1.38 without admins updating the package (if you attempt to use the below methods to upgrade, you will lost all your datas in your wiki), you can build a new site with a new version now.

Steps:
1. Create a mediawiki site;

2. From your LocalSettings.php, copy the followings and save it somewhere safe:

$wgDBname = "x";
$wgDBuser = "y";
$wgDBpassword = "z";

The variable x, y and a are the database name, database username and password respectively.

3. Delete the file “html” and select “delete recursive selected folders” (this will delete all things in your database).

4. Download the latest release of MediaWiki in https://www.mediawiki.org/wiki/Download and save it in your computer.

5. In your empty database, select “select files”, then import the new MediaWiki release you previously downloaded. Remember to select “extract archives” before saving. The file import should take some time.

6. After importing, you will directly see a file name like “MediaWiki-xxx”. Rename that file to “html”.

7. You can now go to your site. You should see something like “LocalSettings.php not found. Please set up the wiki first.”

8. Select “set up your wiki” and select your preferred language.

9. It will then ask you to provide the database name, username and password. That’s when your previously copied credentials makes use. Copy your credentials to the respective columns. The database server is localhost by default, and there is no need to change it.

10. Follow the instructions provided afterthen. You should be able to get your LocalSettings.php file at the end of the setup.

11. Import your LocalSettings.php file inside the html folder.

12. Done. Navigate to your site and the latest version of MediaWiki should be installed.

The methods stated above is tested and worked. A new site with the latest MediaWiki version is installed. Check out the version of my new wiki, it is MediaWiki 1.38.2! ( http://hfhfh.myht.org/index.php/Special:Version )

For users who wants to update your wiki: using the above methods will cause all your data in your wiki to be lost. Please wait until the admins updated the package.

(Edit: this is not true after my investigation. Corrected version: “The configurations will be lost while the wiki site’s data will still be in the database.” As such, I figured out a method to upgrade without Nobu providing the upgrade package. I will soon post the method on a new post. )