Hi @ConnieR68 ,
That is a great question. If the email address you are uploading already exists in the Constant Contact account, the system will upload and update all new information for that email. So, if you have a new name or phone number, etc. for that existing contact, it will be changed when you upload the new spreadsheet. Unfortunately, there is no way to stop the system from doing that.
The only way to bypass updates is by not uploading any additional information for the new contacts besides the email address. If you are only uploading the email address, there will be nothing for the system to update, and therefore no changes will be made to your existing contacts.