Stop using one, start using the other. It shouldnt be an issue, but if you're concerned, do smaller, more frequent water changes at first to 'acclimate' things.
IMO.. there has been a lot of neg feedback on the forum concerning salinity lately... IF you're wanting to change... possibly look into seachem or D&D...
I'm personally a little afraid of Salinity for now I CAN vouch for Seachem Reef Salt though. Just make sure you get the REEF salt, and not the plain "fish only" if you go with Seachem
if you just do regular 10-15 percent water changes it will gradually change out the salt for ya...its not like you are taking all the old saltwater out and adding all new saltwater
I have a bucket I bought 3 weeks ago, used about 4-5 cups out of it for a 20g water change. $40.00 if you want it..... I'm switching back to my old salt.