Gunter,
Be careful, Delcorners isn't always the best solution (well, it all depends on what you're doing). Your curve changes shape with "Delcorners" (you lose your original shape).

I became interested in this problem in 2021. Here's the solution that Michael suggested (link below). This is the method I use; there may be a little deformation, but with practice you'll get a satisfactory result; I'm waiting for a better adapted and more efficient tool from Michael Gibson.

>Hi Zooen, yes currently for that you need to delete the point you don't want and insert a new one. If you want the new one in the exact same spot as the old one you could insert a "point object" (Draw curve > More > pt) at that spot before deleting it so you have a reference to snap on to.

In the future I do want to add in a way to switch from a corner point to smooth point but that is not implemented as of yet, sorry.

- Michael

http://moi3d.com/forum/index.php?webtag=MOI&msg=10404.3