My floor has a 1"crown due to old cinderblock support under main beam in basement. I've set 2 new jacks in place (rated) for 15,000 lbseach, and want to knock out cinderblocks, hoping to correct crown in livingroom floor so I can install laminate . I have one jack on either side of the cinderblock column. Is it safe for me to knock out old support now that the new ones are in place? It's kind of scarey

I am not an expert but I have replaced joists using jacks.
Does your plan meet buildng codes?
If yes:
First, you need good bearing pads for the jacks to sit on. They must be plumb.
Raise the jacks until there is clearance (daylight) above the old blocks.
If the jacks hold to your satisfaction, remove the blocks.
If there is a probem, you should be able to lower backs onto blocks.