SFPs operate at a fixed signaling rate and cannot be changed.
You can verify the operating rate with the "show interface status" command against the interface in question.
we have SFP speeds from 1GB / 10GB / 20_ mgig modules
depends on what SFP you use to connect each other, they will operate on fixed modes.
But if you like to lower them you can make arrangement lower them by configuration(plocy or shaping) . but it can not go above level of fixed rate.