From the Animal Profile:
Click the Add new link in the top-right corner of your screen.
Choose the relevant metric you'd like to update.
A window will appear where you can specify the date the measurement was recorded, and a field (or fields) for the measurement to be entered.
Any calculations will be automatically performed based on how your study was designed.
Once saved, the latest entry will be visible from the list below the graph. You can click any measurement to see who recorded it and when.