To focus on the temperature and magnetic field dependence of the transformation of the vortex structure, systematic and direct investigations on the vortex configuration of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}\phantom{\rule{0.3em}{0ex}}(\mathrm{Y}\mathrm{B}\mathrm{C}\mathrm{O})$ have been performed by scanning tunneling spectroscopy at temperatures up to $90\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and magnetic fields up to $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. At low magnetic fields, we clearly observe a slightly distorted triangular lattice formed by vortices with sixfold coordination, which is attributed to the Bragg glass phase. This lattice transforms into a disordered structure in the presence of a high magnetic field. We observe that the disordered vortices form small clusters comprising fivefold and sevenfold coordination pairs. These microscopically determined vortex structures are in agreement with the vortex matter phase diagram derived from the macroscopic measurements, thus providing evidence of the field-driven disordering transition in the vortex solid phase of YBCO.