how can i use multiple interface constraints with OR not AND

Question

I want to write a extension method to use with 2 interface and wrote this,

public static void Update<T>(this List<T> entities, int index, T newT) where T : class, IDto, IEntity, new()
{
}

it's looks perfect but I have to implement both interface... But I want to implement one of them...

so I try to this

public static void Update<T>(this List<T> entities, int index, T newT) where T : class, IEntity, new()
{
}
public static void Update<T>(this List<T> entities, int index, T newT) where T : class, IDto, new()
{
}

but this time theese methods have got same signature in one code file :)

can anyone help me?

Actually this is not a big trouble "Update1" and "Update2" solve this issue but i wanna to ask already...