If a person apostatizes from Islam, how should they perform ghusl to recite the Shahada?

If a disbeliever embraces Islam, it is obligatory for him to perform the ghusl (ritual bath) of Islam, whether he was an original disbeliever or an apostate. This is supported by what Abu Dawud narrated from Qays ibn 'Asim, who said: "I came to the Prophet (peace be upon him) desiring to embrace Islam, and he commanded me to perform ghusl with water and lote tree leaves." His command implies obligation.

As for the method of ghusl, it is similar to ghusl from janabah (major ritual impurity): The one performing ghusl makes the intention, then says "Bismillah" (in the name of Allah), then washes his hands three times, then washes away any impurity on his body, then performs wudu' (ablution) as he would for prayer, then pours three handfuls of water over his head, ensuring the water reaches the roots of his hair, then pours water over the rest of his body, starting with his right side then his left, and rubs his body, taking care to ensure water reaches all parts of his body and hair.