Remove
Arc weld (arrowed) entire inside circumference of valve seat taking care not to damage cylinder head.
Allow valve seat to cool for a few minutes this will cause valve seat to shrink.
Pry out valve seat with suitable lever.
Clean
Carefully clean valve seat recess in cylinder head.
Install
Press valve seat into cylinder head recess (interference fit).
After insertion cut valve seat with valve seat cutter grind-in valve and seat - see operations "Valve Seat Cut" and "Valve Grind-in".