"Alter" means to make changes or modifications. In this context, it's used to convey the idea of adjusting or changing the outfit to accommodate the person's change in weight.
"Altar" refers to a raised structure or platform used for religious or ceremonial purposes.
"Ultra" means beyond, extreme, or excessive, and it doesn't fit the context.
"Utter" means to speak or express, and it doesn't convey the idea of making changes to an outfit in this context.