There are several free and paid cleaning tools available for your Windows PC. CCleaner is probably the most famous of them all. SlimCleaner is the world's first software that lets you clean and optimize Windows systems using a crowd-sourced approach.
10 Best Tips for WordPress Optimization covers ten things you can do to make your website faster. Among these are installing cleaning up your WordPress plugins and themes, installing caching plugins, enabling PHP and mySQL caching and links to other articles on optimizing Apache etc.