Magnetic Hopfions are three-dimensional (3D) topological solitons characterized by a nonzero Hopf invariant and offer a promising platform for 3D spintronics. While researchers have widely studied their static stabilization, their nonlinear dynamics under alternating magnetic (AM) fields remain largely unexplored. Using 3D micromagnetic simulations and analytical mode analysis, we show that an AM field drives two qualitatively distinct dynamical regimes of a confined magnetic Hopfion. In the weak-field regime, resonant excitation of intrinsic Hopfion modes induces a nonlinear instability and irreversibly reconfigures the Hopfion into a toron. In contrast, in the strong-field regime, the system undergoes reversible field-locked topological switching at GHz frequencies, with the magnetization periodically alternating between a topologically trivial ferromagnetic configuration and a Hopfion state. The driving frequency selects the switching pathway: a 2 GHz field drives a breathing pathway associated with the low-frequency collective response, whereas a 40 GHz field produces a nonresonant rotational pathway governed by strong Zeeman-torque-driven precession and field locking. These results identify field amplitude and frequency as independent control knobs and reveal that reversible Hopfion switching can arise either from nonlinear continuation of low-frequency collective motion or from nonresonant high-frequency field locking.