How to remove relationships between entries
A relationship field expects an array of element IDs. So to remove a user, you'd just get all the current IDs and remove
the one you want to delete.

// Get the current member IDs
$members = $entry-&gt;accepted-&gt;ids();

// Remove a member ID
$key = array_search(52, $members); 
if ($key !== false) {
    unset($members[$key]);
}

// Add a new member ID
$members[] = 83;

// Update the member IDs
$entry-&gt;setContentFromPost(array(
    'accepted' =&gt; $members
));