For "Classic Calendar":

1. go to Settings.
2. click Calendars (tab)
3. click Edit notifications (link)
4. change or remove the default notification setting in Event Notifications and All Day Event Notifications Sections as desired.

For Google's 2017 Calendar:

1. go to Settings.
2. click scroll down the left sidebar to Settings for my calendars.
3. expand the desired calendar
4. click Event notifications or All Day Event Notifications
5. change the default settings as desired.

For "Classic Calendar":

1. Go to Settings.

2. Click Calendars (tab).

3. Click Edit notifications (link).

4. Change or remove the default notification setting in Event Notifications and All Day Event Notifications Sections as desired.

For Google's 2017 New Calendar:

1. Go to Settings.
2. Click scroll down the left sidebar to Settings for my calendars.
3. Expand the desired calendar.
4. Click Event notifications or All Day Event Notifications.
5. Change the default settings as desired.