Well before you go adding a new processor what ammount of memory does the computer have . Adding more memory is usually a cost efficient method of speeding up certain parts of the computers operation
When you say slow what do you mean is it slow when you load more than one program or is it like slow at rendering a video etc
Also if this is a HP when you bought it did you remove all of the HP crapware that comes installed on the computer that usually makes for slow operation
What tasks are you using thic computer for that processor should be able to handle most day to day tasks with little to no slowdown
