Measure the total height of the lally column using a tape measure. Subtract the height of the hydraulic jack and one inch from the total height and transfer the measurement to a 4-by-4-inch wood post. Trace a straight line on three sides of the 4-by-4 post using an angle square so that you can make a straight cut with a circular saw. Cut the post to length.
Set the jack a few inches away from the old lally column and place the 4-by-4 post on top vertically. Push the jack handle up and down to raise the 4-by-4 post to the beam the old lally column is holding. Stop raising the 4-by-4 post once it is snug between the beam and jack.
Place a level vertically against the 4-by-4 post to make sure it is plumb on all sides. Adjust the jack’s position by hitting the base of it with a mallet until the post is plumb if needed to prevent the post from slipping out. Pump the jack a few more times to secure the 4-by-4 post.
Stretch a tape measure out to the length of the lally column and mark it at the middle. Equip a reciprocating saw with a bi-metal blade and cut through the metal column leaving the inside concrete, if present, untouched.
Check the bottom end of the lally column and remove any fasteners. Use a reciprocating saw equipped with a bi-metal cutting blade to cut through the metal column if its base is buried into the concrete floor. Remove any fasteners that secure the top of the lally column to the ceiling area.
Hit the lally column at the center where it was scribed by the reciprocating saw with a sledgehammer until the concrete, if present, breaks. Remove the pieces of old column and place the new lally column in the same spot as the old one; you may have to use a cold chisel to clean up any leftover column concrete before placing the new column over it.
Thread out the top end of the new lally column until the cap is flush against the beam it will support. Place a level on the side of the column and check that it is plumb all the way around. Hit the column base with a mallet to make any adjustments. Drill new holes, using the column bases pre-drilled slots for the correct placement, into the concrete using a hammer drill fitted with the correct size masonry bit; the size will vary depending on the type of fastener you are using.
Place fasteners into the drilled holes and thread them into the concrete using the appropriate tool, such as a wrench or ratchet for bolts, or a screw gun for screws. Hammer nails or thread screws through the column's top cap to secure it to the beam it supports.
Check the beam using a level or laser to make sure it is still straight. Adjust the lally and hydraulic jack as needed to correct any issues with the beam. Locate the hydraulic jack's pressure release valve and turn it to lower the 4-by-4 post.