Select all bolts and then you can change their size via component properties.
Depends on how many different bolts you have, and how many variations there-of. It'll be one operation per variation.
If you have multiple entities of the same bolt, use hole wizard to create the bolt holes, and one bolt (washers and nut). Then use a derived pattern to populate all holes. Then when you change the original bolt (and maybe the washers and nut). It will update all.