(admin)#show platform
(admin)#show hw-module fpd location all
(admin)#install add tar disk0:ASR9K-px9-5.3.4_core.tar synchronous
(admin)# show install summary
(admin)#install activate disk0:asr9k-px-5.3.4* synchronous
(admin)#install commit
http://www.cisco.com/web/Cisco_IOS_XR_Software/pdf/ASR9K_Upgrade_Downgrade_Procedure_IOSXR_Rel_534.pdf