just avoid filling yourC:drive of the computer that is where the Operating system is ,And remove cache and history of the computer ,like doing prefetch ,Temp and %temp% in the RUN may help .And try to remove unwanted files may help you
In addition to what others are saying, I would suggest to upgrade your processor and random access memory. You also need to avoid downloading files that could decelerate the system of your computer.
firstly perform disk cleanup and then disk defragmentation.. after that delete all temporary files and recent files.. this will surely improve your spped.