The front sight is brazed to the barrel and is not removable.
In order to get it off, you'd have to heat the barrel to a dull red heat above 1100 degrees. This will destroy the bluing.
The best option would be to have a GOOD gunsmith cut the sight blade off the ramp and machine a slot in the ramp so a new sight could be pinned in the slot.
A. This won't be real cheap to have done, but it CAN be done.
B. You better be SURE the gunsmith knows his stuff otherwise you'll be having Ruger installing a new barrel for you.
Owners are not happy when the gunsmith isn't as good as stated and the new front sight is crooked because he didn't mill the slot correctly.