- Open the main form in Design View
- Select a subform control (make sure to select the control, not the form it contains).
- Open the control's property sheet and select the name of the new form from the Source Object dropdown.
You will need to perform steps 2 & 3 for each of the 8 subform controls.
If that's more effort than you want, look into the Track Name Autocorrect property in the database options. I'm not sure whether that would automagically update the subform Source Object property when you rename the form object, but it shouldn't take long to find out. Personally I mostly avoid turning on Track Name Autocorrect because it's been reported to cause odd behavior. If you use it, consider turning it on only when you need to rename a bunch of objects and turn it back off afterward.