$userID = 43;
$DEL = 2804;
global $USER_FIELD_MANAGER,$USER;
$user = $USER::GetByID($userID)->Fetch();
$FileInputUtility = \Bitrix\Main\UI\FileInputUtility::instance();
$userFields = $USER_FIELD_MANAGER->GetUserFields('USER');
$control = $FileInputUtility->getUserFieldCid($userFields["UF_FILE"]);
$cid = $FileInputUtility->registerControl($control);
$files = $user["UF_FILE"];
foreach($files as $index=>$id){
	if($id == $DEL){
		$FileInputUtility->unRegisterFile($cid,$DEL);
		unset($files[$index]);
	}else{
		$FileInputUtility->registerFile($cid,$id);
	}
}
CFile::Delete($DEL);
$files["n0"] = CFile::MakeFileArray("https://placekitten.com/500/500");
$USER->Update($userID,["UF_FILE"=>$files]);
$user = $USER::GetByID($userID)->Fetch();