Your best bet might be to take your "Silver Certificates" to a coin/currency dealer, because usually their face value is less that their value as collectibles. Their collectible value will vary based on their date, condition, denomination and more. Because of that you might get different values from different dealers, so you might want to try more than one.
Silver certificates can no longer be traded for silver, but they are legal tender at their face value, so a one dollar silver certificate can be spent just like a regular one dollar bill.
As collectibles, most 1934 and 1935 series dollar certificates are only worth face value or a little more if circulated, and around $3-4 for uncirculated certificates. Ones from 1928 may have a higher value, including:
These prices are approximate and subject to change, so you may want to research a little more on your own before having them valued by a dealer so you can be a more educated seller.