For instructions on upgrading SecureSphere MX and Gateway on Amazon, please follow the procedure located in the relevant AWS Configuration Guide:
WAF-AWS-BYOL-Configuration-Guide -  https://ftp-us.imperva.com/Downloads/SecureSphere_Documentation/v11.5/Imperva-SecureSphere-v11.5-WAF-on-Amazon-AWS-BYOL-Configuration-Guide.pdf
WAF-AWS-On-Demand-Configuration-Guide - https://ftp-public.imperva.com/SecureSphere_Documentation/v11.5/Imperva-SecureSphere-v11.5-WAF-on-Amazon-AWS-On-Demand-Configuration-Guide.pdf