I want to update my PC,how to change into the best PC

If u want to upgrade ur PC to the highest lvl.. XD u'll need a large amount of cash doing dat..

if you have unlimited budget, then get the latest hardware like Quadcore CPU and SSD Harddisk.

It really depends on your extent of usage. Are you a gamer? If you like computer games, you need high specs. Same thing if you are into photoshop and other graphics softwares. For these types of computer activities, you would need a processor that is at least Core2 duo, 2.5 Mhz, 3G ram and 500 gig hard disk. But if you're not into graphics so much, a good computer with these specs: Intel Pentium Dual core (or core2 duo), 2Mhz, 2 gig ram and 320 gig hard disk.

Well if you have the money to spend for the best available pc then you should buy all the new and latest parts that are available. It is common knowledge that computers are known to have new and upgraded versions almost every month it would be best to get the best parts that are available as of the present so that your unit won't be obsolete only after a year.