How to call apex method from a custom button in Salesforce

Apex Class:
global class ApexMethodFromButton {
    webservice static void updateLead(Id leadId) {
        Lead newLead = [select id,Name,LastName,company  from Lead where id=:leadId];
        if(newLead != null && newLead.LastName != null) {
            if(newLead.name.contains('test')) {
                newLead.company = newLead.LastName ;
                update newLead;
            }
        }
    }

}
Custom Button :
{!REQUIRESCRIPT("/soap/ajax/15.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/15.0/apex.js")}

var r = confirm("Are you sure want to update the company?");
if(r == true)
{
    sforce.apex.execute("ApexMethodFromButton","updateLead",{leadId:"{!Lead.Id}"});
    location.reload(true);

}

Output: