You can, but generally this is a feature we only offer to paying partners, and we want to talk with you about it first.
By not offering an upload feature by default, we make sure the email lists you create on the Action Network are 100% opt in, helping keep your mass email out of spam folders. So if you want to upload an existing list, expect us to ask about where the list came from, so we can verify it's an opt-in list.