You can modify your Site Preferences under the Manage Your Account menu:
After clicking Change Site Preferences, the Preferences which you can manage are divided into several categories, which you can jump right to using the Preferences widget on the top right-hand side of the page:
Here we'll take a quick look at Reminders:
Reminders for Client Reviews and Birthdays show up on your Today's Overview page in the Reminders section. You can set up here how far in advance of the date they appear and how many days past that date they remain.