I use espanso now I want to remove it and upgrade to v2.
When uninstalling the old version, some errors come up. What make it a little strange now.
If I run command pacman -R espanso I get the following error: target not found.
But when I run which espanso I can find the espanso in /usr/bin, and it is there.
What should I do now? Can I just delete the espanso in /usr/bin?
Espanso is from the AUR. If pacman had issues uninstalling it (would have been really nice to see those error messages), you can try re-installing it from the AUR, making your package manager overwrite the existing files. As far as I know yay supports the pacman syntax, so you could so yay -S espanso --overwrite "*", which will re-install espanso (the new version) and overwrite any conflicting files it finds during the operation.
Did you install the espanso package, or a related one, like espanso-bin?
https://aur.archlinux.org/packages?K=espanso
If you use an AUR helper like yay, you can search for related packages and see which of them is actually installed:
yay espanso
If you don’t use any, you can also do
pamac search espanso
ok, it’s only the first step. which find application. After, find the package name:
pacman -Qo /usr/bin/espanso
Now we can remove the package.
Note: pacman not remove applications but only packages 
Can I just delete the espanso in
/usr/bin?
Do not do this.
You can search for the exact package name with pacman -Q | grep espanso and then remove it