Hi Tan Yu Xuan, 
I did some digging and found that from Katalon Studio version 9.0.0 onward, the in-app upgrade option was no longer available, and you would have to download the KS 9.x installer file from our website instead …
Here is the download link: Katalon Studio Download Free | Katalon
I will also include the link to the documentation shown above for your reference…
I hope this helps. Let us know if you have any other questions.
Thanks,
Albert