Piwik creates cache files during its normal operation. The caches are automatically deleted in Piwik during an upgrade of core, or an upgrade of a plugin. But in some cases it is useful to be able to delete manually.
To delete all cache files used by Piwik, you can run the following command in your Piwik directory:
Alternatively if you don’t have access to the server and command line, you can delete Piwik caches by deleting all the files and directories inside the path/to/piwik/tmp/ folder in Piwik (the tmp/ folder).