You can access and modify your Site Preferences from the menu available underneath your Name in the upper right corner:
After clicking Preferences, the Preferences which you can manage are divided into several categories.
Here we'll take a quick look at Dashboard Reminders:
Use the Default Reminder View dropdown to select which type of Reminder you'd like to appear as the default on your Today page's Reminders tab.
Reminders for Client Reviews, Wedding Anniversaries and Birthdays show up on your Today page under the Reminders tab. You can set up here how far in advance of the date they appear and how many days past that date they remain.