After the dna binding to the memrane step the kitwill suggest one wash before eluting the pure dna. If you are getting salt carryover then use less of the dirty dna to be purified and do 2 washes after the dna binding step which will wash away all of the salts

If for some reason you have high levels of salt, e.g., you used a CTAB buffer to isolate DNA from plants, then you have a couple of options to reduce the salt. Often the DNA can be precipitated by the addition of ethanol or IPA, assuming the salt concentration is high enough and the pH is around 8. Though spinning it down works, you may lower yield (it is always a mystery as to where the DNA goes!). Another option which will give you better yields is to concentrate the DNA using an ultrafiltration membrane, e.g., Amicon filtration column. Place your DNA in the column, add low salt buffer, and spin it. The buffer pushes through and the DNA stays above the filter. You can use this to remove salts or do a buffer exchange. The nice thing is that the DNA stays concentrated. Which gives us the last option, that being gel filtration with a G25 or G50 column. Gel filtration is easy and works well, but the DNA will be more dilute after passing through the column.

Try washing the DNA with 70% alcohol a couple of times and use the precipitated DNA after drying and dissolving in Tris-EDTA buffer, pH 8.0.