If you are referring to the Playstation Network Online password then without his personal details you will not be able to reset that password. However you are able to reset the PS3 so that it clears all information so you yourself can go to playstation.com and create your own account. You can then select Playstation Network on the newly restored PS3 and enter your own details.
Follow these simple steps to clear all Playstation Network account details.WARNING! You will lose any saved game data and other information doing this!!
Step 1. Turn your PS3 onto standby. (Red light on)
Step 2. Press and hold the power button. It will beep when you first press it, beep about 5 seconds later then beep again and switch to standby.
Step 3. Take your finger off the power button but press and hold it again. It will beep as soon as you touch it, beep again 5 seconds later then beep twice quickly. When you hear this take your finger off the power button.
Step 4. The PS3 will ask you to connect a controller via USB and press the PS button. Do this and then a menu will appear.
Step 5. Select option 5 "Restore PS3 system". This will restore your PS3 back to a clean state so you can put your own details in, for example time and date, console name.
Step 6. On your computer goto https://store.playstation.com/accounts/register/beginNewAccountRegistrationFlow.action
There you will be able to create a new Playstation Network account for free. You can then use these account details on your PS3 when you log in to Playstation Network.
Hope this helps