I assume that you are referring to a PDF file with defined forms fields.
The attributes of the forms fields are determined by the person who actually creates the PDF form.
Your only option is to edit the form definition itself, assuming that the creator of the form has not locked the form in a way that would prevent you from doing such edits (including changing the size and/or location of the forms fields, the font and point size for text in the fields, etc.).
Such forms editing (as well as forms creation) may be done with Acrobat DC. (Reader can fill out and save forms but cannot create or edit forms field definitions!)
But again, be aware that if the creator of the form has protected the form against modification of the field definitions, unless you get the password from that person to remove the protection, you can't edit the field definitions.
Adobe Acrobat Standard is the cheapest application by Adobe that can do that.
Thanks, folks. I know how to proceed now.