To change the date of your games, the event that your team is playing must enable the setting that allows teams to self schedule and change game dates.
Click the "Team Scheduling" tab at top of your page and click on the name of the event.
On the calendar on the right side of you page, click on a day that you have a game. Click and hold the game you are trying to move and drag the game to the "Unassigned Matches" section at the bottom.
From the "Unassigned Matches" section, click and hold the game your are trying to move and drag the game to a new day on the calendar.
You will now see that a game on the new date.