Here are several reasons why you may have to Replace your certificate:
Your Private Key is lost, corrupt or mismatched
You forgot your password or Challenge Phrase (Symantec does not have access to your Challenge Phrase. If you continue to have problems remembering your Challenge Phrase, follow the instructions below to continue with the replace process).
You change server software
You make changes in your server host/key security
You upgrade your key encryption strength
1. Log into each brand Trust Center Account:
2. Select the certificate from within the "SSL Certificate" tab
3. Scroll down to the "Order Summary" tab and under the "Available Actions" select appropriate replace
4. Follow the on screen instructions. A prompt will appear to paste new CSR. Once the CSR is pasted, click continue to complete the process.