There is no configuration option for reducing the spurs. When the LO is applied to the part, it is amplified which increases its harmonic content. Backing off the LO power will at some point cause the harmonic spurs to reduce but with that comes higher output noise. You can also reduce the RF input power to the part but any spur reduction that results from this will be dB-for-dB with the input power, so no dBc gain.