Shazad and Shahzad are two Persian names with the same meaning. They are made up of Sha/Shah (king) and zad (offspring, child). Thus the meaning is "prince", child of a king. This is not an Arabic/Quranic name, but since the meaning is good, Muslims can use it.
Shazad is pronounced as [(SH)ape + m(A)n] + [(Z)oom + m(A)n + (D)ay]. Shahzad is pronounced as [(SH)ape + m(A)n + (H)ill] + [(Z)oom + m(A)n + (D)ay]. Both pronunciations are correct, it is up to you which one you choose.
Shazad can also be spelled as Shazaad, Shaazaad, Shaazad. Shahzad can also be spelled as Shahzaad, Shaahzaad, Shaahzad.