get in contact of the previous owner if you could adn ask him

but most likely you need a professional to Uninstall the Alarm or program a remote [not exactly as easy as people think it is ]

so call up a local Car audio shop or alarm shop who deal's with DEI product's
and see if they might do a roadcall or disconect the batt and hope to god it doesnt have batt backup get it towed to a shop

All DEI alarm's [viper,clifford,python,..etc] have ignition securty so removing the brain would a waste of time