As Nick says, you should just have to slacken the bolts and it will slide off.
Pictures at http://www.lathes.co.uk/boxford-drills/ if anyone else wants to see one. Looks like the lever on the right side is for the tray under the head and the bolt on the left side may be for the column clamp.
Have a look at the general condition of the column first. Take a green scouring pad and some WD40 and clean the column below the head until it looks good. Then drop the head down the column until all the part of the column that is obscured by the belt guard is visible. Clean that part. This should make it slide off easier. They are a tight fit and accumulation of dirt over the years will hamper the removal process. It may be held with a split cotter or the casting may have a slit in it. You can drive a wedge into the slit if it is difficult to move but be very gentle. You are not trying to prise it apart but just resisting any tendency of the casting to spring together.
You have to assess how you will reassemble it before you disassemble it. You need sufficient headroom above the top of the column when it is sat on the bench for the body of the drill and your lifting apparatus. If you do attempt it this way, screw the base to the bench before you install the head. It is one less thing to be moving about on you.
I would be tempted to drop the table and head as low as they will go on the column, sit (screw) it on a sheet of plywood and crib up each side a little at a time until it is level with the bench and then slide it over. A bigger sheet of plywood means there is less tilt of the drill for a given increment in height.
Edited By DC31k on 09/04/2020 10:30:54