When do you stop using an infant insert? I am using the ergo infant insert

The weight are given as a guideline. You will have to see that baby is able to achieve knee to knee without having hyperextended legs then you can stop using an infant insert. Ergo baby infant insert is rather thick and hot, you can remove the back panel once baby have good neck support and just use the "seat" until baby is able to achieve knee to knee. Left is legs hyperextended. Right is the correct knee to knee.