The energy and structure of two-dimensional domain walls under the action of an external magnetic field directed perpendicular to the easy axis of the film are investigated based on micromagnetic modeling. The transitions in the domain wall structure are considered in detail: with an increase in the external field, the transition of a single-vortex 180° Bloch DW to an intermediate two-dimensional Neel DW and, after removal of the external field, a transition to a 180° two-vortex structure.