Can i upgrade pentium 4 without change mobo

I don't think you can. Only with 775 socket like bambam said but it's rare. Always chose custom made PC with upgradable motherboards.

depends on which Pentium 4 you currently have..................... if its LGA775, then you have some decent options such as the Core 2 Quad Q6600 (imo most stable processor ever made)........... if you want to do some serious gaming then you will definitely have to upgrade to an 1155 (if you like Intel chips) or at least an AM3+(if you like AMD chips).............. I still run an AM3+ chip, an AMD FX-8350 OCd to 4.9 GHz