what do you currently have?
Brand
OS including any updates
MOBO
CPU type
CPU speed
FSB speed
maybe you just need to run a few programs across it like CCleaner and Belarc advisor and a do full disk defragment
Do you mean software as in DAW & VST's or operating system?what software do you currently have installed?
but yes this is eminently cleanable and still very usable
given that you are running 8 just use CCleaner to begin with - let it deal with all the options simply to give your pc a good deep scrub of out of date cache files and temp/tmp files
once it is done download and run mydefrag using system disk monthly as the setting - this will reorganise your drive and remove all fragmented files which may be causing some of your experienced kludginess