Plots are layered according to is plot number, with Plot 0 on top, i.e. Plot 0 overlays Plot 1, which overlays Plot 2, etc.
The only way to bring a plot to the front is to reorder the plots so it is Plot 0.
In the attached example I have three waveforms, using a cluster of its to keep the Name, Color, and Y-Data together. I placed these clusters in an array for easy manipluation, using toggle switch and "Reverse 1D Array.VI" to swap the order of the plots. The plot name and color are unbundle and written to property nodes so the legend matches the plots.