I don't know as much as john, so he can correct me if im wrong, but I don't understand why people have so many problems with this sort of thing.
Like most things computers need maintaining too and a bit of common sense goes a long way. Do a scandisk once in a while and if you had a HDD do a defrag after, its like reorganising your office and papers, so you can work more effectively and your not hunting around looking for stuff. Other than anti-virus software or something like malwarebytes, you don't need anything else to look after your PC.
There are other reasons for a slow PC, e.g component malfunction, a full hdd, an aging PC which just does not have enough performance to run more modern programs, speed up software would never work in these circumstances, if ever.
Also don't download crap from websites that you don't know are 100% legit.