Over the last week Google announced that they were going to stop supporting the SHA-1 algorithm for signing certificates.
Google’s SHA-1 deprecation announcement
Because of this I have created a couple of posts explaining how to migrate to SHA-256 based signatures.
Generate an OpenSSL Certificate Request with SHA-256 Signature
Change OpenSSL Default Signature algorithm
Since I wrote those pages other security companies have started to post their own migration strategies.
Qualys SHA1 Migration: What you need to know
In addition, all the major Certificate Authorities (CA) have started providing customers information specific to their services. So if you have certificates already, then contact your CA for further migration help.