For many applications of Vertical-Cavity Surface-Emitting Lasers (VCSELs) it is important to obtain high power of emitted light. Due to the laser thermal properties that limit maximum current density in the active region, high power emission requires large laser apertures. This results in appearance of multiple transverse optical modes, which very often are undesirable. In the talk we present important aspects of modeling these modes with advanced self-consistent software and we will also show some propositions of possible measures that can be taken to increase modal selectivity and reduce number of modes. We illustrate these general concepts with examples of modeling gallium-nitride VCSELs.