Praise be to Allaah.

Changing from tamattu‘ to ifraad is not permissible and is not possible. It is only permissible to change from ifraad to tamattu‘, in the sense that if a person had entered ihram for Hajj ifraad, then after that he changed his ihram to be for ‘Umrah, thus it became tamattu‘. Similarly, in the case of qiraan, it is permissible to change one’s intention from qiraan to ‘Umrah, thus it will become tamattu‘. This applies except for the one who has brought his sacrificial animal with him in either case, in which case it is not permissible for him to do that, because the Prophet (blessings and peace of Allah be upon him) instructed his Companions who were with him to change their ihram for Hajj ifraad or qiraan to ‘Umrah, so that it would become tamattu‘, except for those who had brought a sacrificial animal with them. End quote. 

Majmoo‘ Fataawa Ibn ‘Uthaymeen, 22/88, 89.