Serine, with so little information about your system, your connection type and speed, and what you mean by downloading speed, there is not much we can tell you.
What System do you have, eg What Operating System, XP with SP2?
What Processor speed?
How much RAM?
How large is your hard disk? How much space is used up?
What type of internet connection do you have, eg Dial-up, DSL, Cable, Wireless? What speed?
What do you mean by download speed? Web Pages?
What do you mean by PC speed? Slow startup? Slow opening of programs? Videos running slow? (What type of videos and what do you use to watch them?)
What type of Optimisers are you using?
Do you scan your PC to keep it clean of viruses, and spyware? If so, what do you use?
How can i Boost up my PC speed and downloading speed,
Although i used some Optimizers but it also occupy my disks memory spaces and speed down the OS similarly for Booting Time.