It happens to us all, one minute we are sprightly and fast and the next slow and lethargic, this is also true for operating systems. Ultimately when operating systems get cluttered the best solution is a reinstall but before being so radical running clean-up software may buy some time and speed.
CCleaner comes as a free download and after 14 days you have the option to purchase the full version or continue running a limited free version. There is a professional version with greater functionality (comes with defragmentation, file recovery and hardware analysis tools), a cloud version and extensive business support.
This system cleaner remains the most popular on the net, mainly due to its simplicity of use and reliability.