If you're very unlucky, when you install Divi Booster you may be met with a "mkdir(): Permission denied" warning.
To fix this, please ensure that the /wp-content/uploads directory is writable. This can be done by setting the permissions level on the folder to 755 (or similar). You should be able to set the permissions on the folder using either an FTP program, through your web host file manager, or using a WordPress security plugin (you may already have a security plugin installed which is restricting the permissions in the first place).
For more information on file permissions within WordPress and how to change them, please see: Changing File Permissions