how delete all the information in my computer

Boot to either the included OS X reinstall disc that came with your Mac, Mac's produced before OS X Lion came out, or from the built in or Online Internet Recovery system and erase the Macintosh HD partition. Or you could Re-Partition the drive as One partition and that will remove everything also. You do either from Disk Utility once you have booteb from some other source than the internal drive.

Erase and reinstall OS X

http://support.apple.com/kb/PH11273

http://www.thesafemac.com/how-to-reinstall-mac-os-x-from-scratch/

Reset your Mac