Usually it's printed on the bottom of the laptop or near the keyboard(Model number) The cpu can be found out by right clicking on my computer and then properties it sould say something like 'Core 2 duo @2.6ghz'. Also do you know what GPU it has? you can check by downloading and running this.
Either take it apart yourself or bring it to a tech shop and have them take it apart to see if the CPU is soldered to the mobo. If it is there is nothing you can do. If it's not you can probably change it but you'll have to check with the manufacture for an approved CPU support list.