http://www.piriform.com/ccleaner
Or download the portable version from
http://download.cnet.com/CCleaner-Portable/3000-2086_4-75182000.html
Once you install it,start the software from the programs menu.It has two options on the cleaner screen to switch between windows and applications.Select the options you wish to optimize.After that click the analyze button and once it shows Analysis Complete message,click on run cleaner button as shown below
Next icon on the left side menu is for registry cleaner,once you click on that it shows the options on the right hand side.Click on scan for issues and after its complete click on fix selected issues button(Once you click on that it asks if you would like to backup changes to the registry,its strongly recommended you click on yes and create a backup) as shown below
Next option on left hand side is for tools,clicking on it would show sub menu with uninstall,startup,system restore and drive wiper options.The uninstall option is to remove any application like you do using add/remove or program & features options in control panel
Next is Startup using which you may select the softwares & services that you wish to enable,disable or delete on computer start (If you are not sure of any software and service,dont configure it else you may endup with no boot atall).Below startup there is system restore option using which you can delete any previously created system restore point if you dont want it anymore.Next is drive wiper using which you may free space on any drive or can erase data from the entire drive
Its the best free cleaner for your computer,if you know about any other good registry cleaner and optimization software do let us know so that we can inform our readers