How to remove all users from a role? How to remove all users and their content from a specific role programmatically ?
Here are some quick code examples that I have used to add or remove user roles in Drupal 6. This can be very helpful if you are building a module for a specific site that has to manipulate user roles. Using this technique is not the most flexible solution as it limits itself to the roles configured on a specific site (based on role id and role name). However, you could easily add a database table and an administration section and make this more flexible if needed.

Here is an easy way to add a role:

//you will need to enter the uid of the user here, I am just using user 1

$user = user_load(1);


//first we check if the user has the role in question (using the rid of the role)

if (!isset($user-&gt;roles[7])) {
    //if not we add the role and set the role name based on what is entered
    //in the drupal role administration section
    $user-&gt;roles[7] = 'role name seven';
}


Here is an easy way to remove a role:

//you will need to enter the uid of the user here, I am just using user 1

$user = user_load(1);


//first we check if the user has the first role in question

if (isset($user-&gt;roles[8])) {

  //if so, we unset the role
  unset($user-&gt;roles[8]);

  $edit = array('roles' =&gt; $user-&gt;roles);
  user_save($user, $edit);
}


Here is an easy way to do a role swap:

//you will need to enter the uid of the user here, I am just using user 1

$user = user_load(1);


//first we check if the user has the first role in question

if (isset($user-&gt;roles[8])) {

  //if so, we unset the role
  unset($user-&gt;roles[8]);

  //now we check to see if they have the role we want to swap for
  if (!isset($user-&gt;roles[7])) {

    //if not we add this role
    $user-&gt;roles[7] = 'role name seven';
  }

  $edit = array('roles' =&gt; $user-&gt;roles);
  user_save($user, $edit);
}


check this link for more info my post
 How to remove all roles from a user?