Log into your Google account and go to your Calendar screen. Find the event you want to change, select it and click the “Edit event” link. On the page for that event, change the time, location and any other information that needs to be updated. You can also invite more guests, add a video call or request a timed reminder from Google, so you remember the event yourself.
When you click the Save button at the top of the page to seal in the changes, Google Calendar presents you with a pop-up box asking if you would like to send an updated invitation to your recipients. Click the Send button to notify your guests of the change.
For those new to Gmail, you can send invitations for meetings and other events by first creating and addressing a message to your potential attendees. (You can also create an invitation to accompany a reply or a forwarded message.) When you have the addresses added, move the mouse cursor over the + button in the bottom toolbar and click the Insert Invitation icon, which looks like a tiny calendar.
When the Invitation box appears on screen, fill in the details and click the Insert Invitation button to include it with your message.
source : Times of India