The sender is usually a little plastic tube that fits into the top of the fuel pump, which itself fits into the fuel tank. Each one has a connector going to it (power for the pump and sensor for the the sender).
You can unscrew the sender and lift it out without disturbing the pump... though having said that, the sender unit is made of a fuel-resistant white plastic that becomes brittle with age and is often reluctant to come undone (twist 90-degrees and pull out) without the little tangs on the top breaking off and it being a royal PITA...
Nevertheless, it can undo and lift out.
The float looks like a circular piece of plastic (the float) attached to a plastic lolly stick. It's really not a precision engineered brass or metal contraption (though you may have been expecting one, given the price). Put it in the recycling bin and fit a new one, since by the time you got that far, it's not worth replacing the old one.
That ought to fix it, for a while at least..
though having said that, the one in my 155 went for 18 years and was still fine... just happened to break when I was removing it to fit a new pump (pump won't come out with the sender in place).