Go to your contacts. Select the 3 dot menu at the top of the contacts list. Select "manage contacts", then "move contacts". A list will come up of where you can move your contacts to and your Google account should be one of the options. Select your google account. After the contacts are moved, you can go back to the manage contacts menu and merge your contacts which would remove any duplicates and merge their information.
If they are in your Google account, you can access your contacts from anywhere by going to contacts.google.com, where you can view them, edit them, delete or add any contacts. They will also transfer from phone to phone as long as you are signed into your Google account. Once they are in your Google account, whenever you add a contact in your phone, it will be part of your Google contacts.
