Edit>Delete Guides works wonders.
Make the components in that bench unique so you don’t modify the instances in the others. Then I expect you’ll find it easier to just edit the components, draw vertical lines and use Push/Pull to get rid of the waste. If you want to cut the components with Intersect faces, draw a vertical rectangle as a cutting plane, cut it to the clipboard and then open the components that need cutting one at a sime, use Edit>Paste in place to paste the cutting plane, followed by Intersect Faces. Then erase the side you want to get rid of.