The good news is you can do this! You can merge multiple contact lists directly through the Contacts Tab of your account. This can be done through 5 simple steps:
Hope these steps helped!
I have more than 10k contacts in one of the lists, so Constant Contact won't let me. If you can think of another way around this, that would be great.
Thank you for following up with us on this! You are correct, this merge feature is not currently available if you are trying to merge more than 50 lists or any lists with over 10,000 contacts. Though we are no longer making updates or changes to the current Contact's experience, this is a feature request we are collecting feedback on for our New Contacts Redesign experience. In the meantime a workaround you can try is exporting your list and re-uploading it into the correct list. I apologize for any inconvenience this may cause.
You're very welcome! I'm glad we could help point you in the right direction. Feel free to reach out to the Community again if you have any further questions.