These are programs I use and trust to clean computers and speed them up. All programs are free, but do have paid versions or trials as stated.
Malwarebytes - Use free version to clean up slow infected systems of junk ware.
CCleaner - Use this free program to clean temp and Reg files to help boost performance.
Hitman Pro - Use the 30 day Trial to clean a system if really bad, I use many programs to clean a PC.
SpyBot - Search & Destroy is a free malware removal tool provided by Safer-Networking Ltd.