If your site is located on a virtual (shared) hosting, then the problem with access rights almost never occurs, since the hoster always configures the general server correctly. If you have a dedicated server and have problems with access rights during installation - most often this happens when the owners and groups of scripts and FTP do not coincide. At the time of testing, you can install these folders and rights files 777 recursively (this is a temporary solution) to ensure that the problem is caused. Then it is still recommended to figure out why such a situation arose. Completely helps the command chown , you can show this part of the text of the Hoster or the administrator serving your dedicated server - they will immediately understand what's the matter. In extreme cases, you can resort to manual installation, the process that enters the instructions for modules and plugins.