AmiKit for Raspberry Pi uses 64-bit Manjaro XFCE distro.
To update Amiberry, download the corresponding build from its website https://blitterstudio.com/amiberry/
or GitHub to be precise: https://github.com/BlitterStudio/amiberry/releases
There you can report any issues you have with Amiberry too and help its development.
The Amiberry folder in AmiKit Manjaro XFCE linux distro is located in home/amikit/ folder - as far as I can say from top of my head.
Just make sure to backup the old folder and/or entire card before you start experimenting on your own.