What kind of change do you need to make? You can make changes that don't involve adding or removing a question without needing to replace the existing form. The kinds of changes you can make are:
- changing the text or translation of a label
- changing validations, calculations, relevants
- changing options for a
selectorselect1
Questions can't change type and the form title and ID have to stay the same. If that's the kind of change you want to make, you can update the version and re-upload the form. If you're using XLSForm, you can read about the version field and changing it here.
If you need to make a deeper change, I also do what @A.N.M_AL-IMRAN describes.
EDIT: https://docs.opendatakit.org/form-update/ now describes the update process in detail.