Rule 15. Amended and Supplemental Pleadings

(a) Amendments Before Trial.   
    (1) Amending as a Matter of Course.  A party may amend its pleading once as a matter of course:
<>        (A) 21 days after serving it, or
        (B) if the pleading is one to which a responsive pleading is required, 21 days after service of a responsive pleading or 21 days after service of a motion under Rule 12(b), (e), or (f), whichever is earlier.
    (2) Other Amendments.  In all other cases, a party may amend its pleading only with the opposing party’s written consent or the court’s leave. The
    court should freely give leave when justice so requires.
    (3) Time to Respond.  Unless the court orders otherwise, any required response to an amended pleading must be made within the time
    remaining to respond to the original pleading or within 10 days after service of the amended pleading, whichever is later.