§1. Upon certain notice of transfer, a bishop must claim the diocese to which he has been transferred (ad quam) and take canonical possession of it within two months. On the day that he takes possession of the new diocese, however, the diocese from which he has been transferred (a qua) is vacant.
§2. Upon certain notice of transfer until the canonical possession of the new diocese, a transferred bishop in the diocese from which he has been transferred: 1/ obtains the power of a diocesan administrator and is bound by the obligations of the same; all power of the vicar general and episcopal vicar ceases, without prejudice to can. 409, §2; 2/ receives the entire remuneration proper to this office.
Source: Code of Canon Law (Vatican.va)