--force option for the
install action just overwrites any existing files on disk if the packages you're trying to install already exist. It doesn't remove files from disk like the
uninstall action does.
I'd do the
brew uninstall imagemagick first before doing an
brew I find the simplest approach is often the best: I want to reinstall something then I should remove it first with
uninstall and put it back with
install. The homebrew sandboxing does a very good job of making for clean uninstalls from your system.
If you wanted to uninstall it by hand you'd just need to look in
/usr/local/bin for any files that linke to
../Cellar/imagemagick and delete those symlinks. Then delete
/usr/local/bin/imagemagick and it's gone. You may be left with some dependency packages that also need removal, but the core imagemagick package will have been deleted. To see what imagemagick depends on if you want to do further cleanup run:
$ brew info imagemagick
Depends on: jpeg, libtiff, little-cms, jasper
Some tools will complain unless the ghostscript fonts are installed to: