High energy emission from pulsars is thought to be primarily driven by magnetic reconnection as well as plasma pair-production processes that occur in the corotating plasma-filled magnetosphere. Constructing an accurate description of the plasma kinetics in the magnetosphere is therefore crucial for understanding how pulsars emit electromagnetic radiation. We will use the well-established Particle-In-Cell (PIC) method to accurately capture kinetic plasma mechanisms underlying the large-scale dynamics of the pulsar magnetosphere. WarpX is an electromagnetic PIC code, which was primarily developed as part of the Exascale Computing Project for modeling plasma wakefield accelerators. We present our preliminary work on extending WarpX to investigate the three-dimensional structure of pulsar magnetospheres. The highly disparate length-scales that span the pulsar magnetosphere renders uniform grid simulations intractable for a realistic system. As a result, the magnetic-field is typically scaled down to allow for accurate resolution of kinetic scales. We thus study the effect of scaling-down the magnetic field strength on the spin-down rate predictions from the simulations. We also present the advanced numerical algorithms in WarpX that can be leveraged to explore the use of mesh-refinement for efficiently resolving the kinetic length-scales in pulsar magnetospheres.