I suggest you use the unsalted butter. Baking experts say using unsalted butter allows you to control the salt in your recipe and it is also relatively fresh (because they spoil easily). Unsalted butter also plays a great role in your baking result.
No, unless you heat the butter in water first then allow it to cool with the water until the butter solidifies. Take the butter and throw away the salty water. It is much easier to go to the shop and buy the unsalted butter.
I sometimes substitute salted butter & have not noticed much difference in the results,however Micks suggestion to melt the butter in water & throw away the salty water after it has solidified seems like an option worth trying.I always buy butter when it is on sale & freeze it,as unsalted is often not on sale I usually end up with salted most of the time.