I got this mail from Apple.
Your iOS Distribution Certificate will no longer be valid in 30 days. To generate a new certificate, sign in and visit Certificates, Identifiers & Profiles.
I get some information from StackOverFlow but I want to know what I need to do if I modify my existing app. Will I able to update in future the same app with new certificate and new profile. Is that I need to revoke and generate the new certificate. Thanks for your help and comments.