Remove item level permission for specific user using powershell

I want to remove the permission for each item and then want to add my unique permission I have tried the code for giving permission. But firstly, i want to remove it and then add new permission. My code is as below:

    $clientlist.Items | ForEach-Object{

         $contentTypeName=$_.ContentType.Name
         if($contentTypeName -eq 'Proposal')
         {
                $clientlist.BreakRoleInheritance($True)
                $userNew = $webNew.EnsureUser($user)
                $roleDefinition = $webNew.RoleDefinitions[$PermissionLevel]
                $roleAssignment = New-Object Microsoft.SharePoint.SPRoleAssignment($userNew)
                $roleAssignment.RoleDefinitionBindings.Add($roleDefinition)
                $clientlist.RoleAssignments.Add($roleAssignment)
                $clientlist.Update()
                Write-Host "Successfully added $PermissionLevel permission to $UserNew in $clientlist list. " -foregroundcolor Green
         }
}

Thanks.