How do you remove....

Kodiak, (any relation to Rupert?) I use two methods either meths on the end of a cotton bud rudded very gently or a curved scalple blade held at right angles to the loco body and rubbed over the number. With the latter it's important to apply no pressure and just let the weight of the knife do the work.
It is probably a good idea to remove the whole number as an exact colour match with the factory applied numbers is unlikely. Of course a bit of weathering can hide a multitude of sins so a colour match is not that important if you weather.
Good look and lets see the results.

People use sugar to get the orange logo off phones. They just put the shugar on the logo with a little bit of water and rub it and the abrasive qualitys of the sugar crystals scratch the paint off wihtout damaging the phone....

Might work....

I've used a soft white pencil eraser to remove lettering from American Bachmann passenger stock, and it worked very well.

While i have not used this tecnique on railway models I have applied it to die-cast buses when nodifying them. Ladies nail varnish gently stroked on with a cotton bud.

Regards