Are your neighbour spaces all full up?
Do you want to add more neighbours?
Do you have a neighbour who does not play any more?

Below are two ways to remove a neighbour: 

1.  Load your farm and click on the neighbour you wish to remove. Select "Remove Neighbour" from the pop up menu.

2. Load your farm and click on the "Neighbours" Tab at the top of your gaming screen. The Blue highlighted names are your neighbours. Click on "Remove Neighbour".

On this page you can see if they are (Active, when they last played, which level they are at, XP amount, coins amount, best diversification and help given to friends) 

You can also "Add as a Neighbour"