Cisco 4500 IOS XE upgrade with ISSU

Checklist:

• auto-boot must be enabled
• SSO must be configured and standby supervisor engine in STANDBY HOT state
• NSF must be configured and working properly
• Current running IOS XE must support ISSU
• 
  

For detail, refer this http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/3.1.1SG/configuration/guide/issu.pdf