Ravi Gagan :
Still I will say dont try
I tried with my Pentium Dual core desktop, it was a mess. I had to roll back to Window 7 again
Accepted there's a risk, to be honest you can 'Clean Install' the Pro Upgrade to get best results. A lot depends on what you're upgrading from, if it's 7 Pro then there's not much to be gained, but an upgrade from Vista would be most desirable, then again if you're running your OS on an SSD then 8 is faster, lighter and uses less resources. Personally I've found the best improvement for the money is to replace HDD with SSHD, no great improvement in actual performance, but boot and load times are drastically reduced...