How can one edit map service legend (raster layer)?

[PiotrIwaniuk]

I have the raster layer in my map service, which is automatically created by asynchronous GP service as its output result ("View results with a map service" option). The raster is symbolized with graduated colors and then the whole map is exported along with its legend to PDF using printing service. The thing is that the symbol for the legend according to rest output looks like this:

Layout in PDF is even worse, probably due to transparency options in map (PNG32 is fine though):

The question is: Can I change its look somehow? I'd like to rename or get rid of labels (I need it in Polish) and I want one rectangle instead of three split boxes.