Various ways:
1. XMLHttpRequest
2. ASP.NET AJAX (Using Update Panel)
3. PageMethod
4. ClientCallback
Pick the one that suits you and Google it. You will get enough links to read/know about them and implement it.
P.S.: Have not written anything on [Ajax.AjaxMethod], as I think it's quite old and no more supported in current ASP.NET application. If you are specifically looking for that then this article should help you out:
AJAX in Action[
^]