New door in basement wall

[Larsa]

I'm considering installing another door in the basement. There is currently a window where the door is supposed to be. The wall is made of some kind of stone material (the house=1907, but this particular wall is not natural stone but rather built and plastered, probably from the 1940s).
Since there is already a window there, I shouldn't need to worry about installing a lintel above the door, right? I'm planning not to make the door wider or taller than the window, just chiseling out below the window down to the floor.

By the way, the floor joists in the floor above are wooden.

 

[Immobil]

Just bring out the big angle grinder with the right disc. Draw lines and cut with all your might.

 

[Starfighter]

Don't forget the protective mask as it's likely to get really dusty!

 

[Mats]

Just remember to start a little sparingly. It's always easier to carve out a little more than to put plaster and masonry back if you take too much.

 

[ByggaNytt]

If it's built with some form of lightweight concrete, you can also use a reciprocating saw with the right blade or hand saw with a lightweight concrete saw (like a handsaw with big teeth).