The i5-2400 is quad core.
That said, what exactly is slow about it? Particular games? Particular applications?
Do you also have a regular HDD to go with the SSD you have? I think having a total of only 224GB of storage could hurt the system as you could be running out of space; you'd have to religiously keep up with cleaning up temp files, downloaded updates that have already been installed, etc.
If gaming seems slow, what resolution and refresh rate is your monitor?
"Somewhat slow" is kind of vague, we'd need more detail as to what the issues are.