In the layers panel, click on the circle that is half filled at the bottom of the panel. This will bring up the layers adjustments. Select levels from the menu.
In the properties panel (window>properties) you will see a histogram in the middle of the properties panel.
Just below the histogram are three triangles. Left is shadows, middle is midtones and right is highlights.
Drag the right slider inward towards the middle triangle to force the hightlights to become pure white. (Stop when the pointer points to the change of the histogram - that is where there is data and you don't want that to be pure white)
Drag the left slider inward towards the middle triangle to darken the shadows by forcing those shadows to be pure black. (move in only a little to your taste since the histogram starts at the beginning - if it had a gap like it does on the end, you would want that removed by sliding past that part)
So what you are basically doing is stripping the non-existent data from the histogram to increase the contrast. As it allows the data to expand.
Doing this forces the blues to become white