How old is the computer?
Is it a Mac or PC?
What OS are you using? (Kind and version) If it's a PC are you running windows or unix?
What processor is in it, and what's the clock speed?
How many hard drives are present?
How big are they, and how much free space is on each?
How much RAM is installed?
What does it do that you think is too slow? (What programs and/or processes don't respond as rapidly as you want?)
What AntiVirus/AntiMalware do you use, and IS IT UP TO DATE?
Is it a single computer or do you have a multi-computer LAN?
What kind of internet connection are you using? Modem/switch/router? Wired or wireless?
What kinds of peripherals are connected?

As the question is stated, the only reasonable response I can think of is to suggest you drop it off a tall building. I can assure that it will speed up all the way down. That might not be what you had in mind(?). If it's not, you need to finish the question.

John