FIG. 1 is a left side perspective view of a denim boot upper, showing my new design;

FIG. 2 is a right side perspective view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side elevational view thereof; and,

FIG. 6 is a right side elevational view thereof.

The broken line showing of a sole and heel in FIGS. 1-6 is for illustrative purposes only and forms no part of the claimed design.