Hello,
I bought this Chinese tablet for my family - Chuwi Hi9 Air, His software really bad, very slowly.
the problem he came with Android 8 and not really been updated for a long time.
I found this guide online:
In fact, there is software or method to update Android 9 or other version in an informal way, do you recommend to use this guide?
I don’t understand that much in android system… and would like your help. Because i don’t know if its dangerous and I do not want and just afraid to completely destroy the tablet.
Well, custom firmware can be very good, also it’s really hard to “brick” devices with MTK cpu.
If you have no experience in flashing and changing official roms to custom - MTK is really good choice to practice 
Just follow the instruction and everything must be fine.
Thank you for your response,
Yes you’re right and I have no experience and knowledge of it. The truth is that I am an iPhone customer at all
Can you explain about the process? For example, what is the MTK expression you specified?
I’m terribly afraid to get stuck in the middle of a manual or not know what or how to do and destroy the tablet
MTK cpu is really good in recovering after any mistakes and it’s really hard to break bootloader in devices with this processor.
You found good guide, so just follow step by step.
Thanks, but I noticed that the guide is out of date because version 17 has been released and all downloads are not valid, Now I don’t know what kind of version to download.
In addition, I couldn’t figure out how to install TWRP Recovery
I tried searching the internet but didn’t find much information about it
TWRP guide.
In this thread you can find some information about custom roms. I can’t recommend to you any rom because i don’t have this tablet and can’t test them.