call.js

Meteor.call('changeSettings', settingsDoc, function(err, result) {
    if (err && err.error === "not-admin") {
        console.log("Unable to update settings, not an admin!");
    } else {
        console.log(result);
    }
});

method.js

Meteor.methods({

    changeSettings: function(doc) {

        console.log("Update method called.");

        var currUser = Meteor.user();

        if (!currUser || !Roles.userIsInRole(currUser, ['admin'])) {
            throw new Meteor.Error("not-admin", "User is not logged in, or is not an admin!");
        } else {
            theID = Settings.findOne();
            console.log("Updating settings doc with ID: " + theID);
            return Settings.update(theID, { $set: { start: doc.start, end: doc.end, timeSlots: doc.timeSlots }});
        }
    }

});