I myself am partial to a fixed sidebar, so yes :)
In the code you’d need to find the .class (in the CSS portion) that corresponds to the sidebar… Some coders like to get creative in how they name it. Then you’d need to set the position to ‘fixed’ (sometimes it’s absolute, sometimes it’s relative). It’s a little complex if you’re not familiar with coding.
Something else to be careful about: When you change positions of certain elements in a theme, it can screw up the margins of the elements that come after it.
Good luck :)