Plugin W3 does not show… how to delete or reinstall?

I get a W3 total cache error that makes it impossible to upload pics to my blog. The error says to delete or reinstall the plugin, but trying to reinstall I am told that the plugin is already there. However it does not show under “plugins”, so how to uninstall first. I looked through some supportlines but did not get any wiser.

How can I solve this in a simple way? If W3 is installed how can I get it to show up?

https://www.ads-software.com/plugins/w3-total-cache/