Sweating off sights can be very tricky and if not done right can damage the barrel.
Most just leave them on because after sweating them off you will have to re-finish the barrel and also the chance of ruining the barrel.
If it must be removed, Turning it off on a Lathe is the safest way but you still have to re-finish it and re-crown when you are through while it is still in the Lathe.
Some sights are low temp solder and they may come off easy but others are high temp soldered and can definitely be risky.
Some people simply cut off the barrel behind the site. This is ok if you have a cartridge that does not need a long barrel for its use. (Lots of cartridges do fine with a 18 to 22" barrel). But it still has to be crowned.
I have done this, JE is correct, if it is soft solder, you can proceed with little risk to the barrel, you can also proceed if it is silver solder with caution, a slow heating approach is needed with either and as soon as the solder bubbles remove the flame and tap off the sight with a brass drift os suitable size and weight. It may be necessary to heat and move the sight in steps, as the solder solidifies quite quickly when the heat drops. If you're uncomfortable doing this, I would get a gunsmith to do it.
Sometimes I have to remove the front sight to install a muzzle brake if the owner does not want to shorten the barrel. I set the barrel up to install the brake, use the tail stock with a live center in the muzzle to steady the barrel while removing the sight, thread the tenon and time the brake. Contour the brake to the barrel and remove any signs of the site, once this is done I remove the brake and re-crown the barrel, re-install the brake and finish the barrel and brake treatment.