Hi Mihailo,
Follow this steps:
ASA(config)# boot system flash:\asa-842-k8.bin
ASA(config)#asdm image disk0:\asdm-645.bin
ASA(config)# write memory
After this reload the firewall, it would come up with 8.4.2 and then open a browser window and type in https://
select install and run option, it should now pick up the new asdm.
Hope that helps.
Thanks,
Varun
Thanks,
Varun Rao