Click the "Download Here" link from the Set Up page on the Fitbit website to download Fitbit Connect. Set up a Fitbit account, and use the Wireless Sync Dongle that comes with the Flex to sync it with the computer. Change account settings from the Dashboard.
Once you download Fitbit Connect, right click the icon, and select "Open Main Menu." Choose "Set Up a New Fitbit Device." This takes you to a screen that allows you to either log in to an existing Fitbit account or create a new account.
If you are new to Fitbit, enter your information to create a new account. If you already have an account with a different Fitbit device connected to it, you will need to replace that device with your new Fitbit Flex, as only one device can connect to an account. If you don't want to replace the old device, set up a new account for your Flex. The program asks you for details that help calculate your calorie burn.
Choose "Flex" as the type of device you're registering. The program prompts you to charge the Flex before inserting the Wireless Sync Dongle. When you click "Next," the program connects to the Flex, which is indicated by flashing lights. Tap the Flex twice to make the device vibrate. This means the device is finished connecting.