Deleting faces??

[micheus]

It seems like you may have a bad topology there because Dissolve should to remove those vertical faces connecting the horizontal extension of the chair.

You can try - in orthographic [o], Z view [z] - use the marquee selection to select the edges/faces in between those horizontal "bars" and then use Dissolve [DEL].

Sometimes, you can also use Clean in body mode to remove any small ("hidden") face/edges that may avoid some commands to work properly.