Remove all the crown molding, and frame in the arc, sheetrock and paint it so it's gone.

Actually it is made of cement and rmoving may actually increase cost nd may hsmper strength

That is a lot of work , about working with it instead, the architecture and design are great .It looks like .the arch is very
thick ,if you were to square everything off it will surely remove the softens of the curves .
May I ask what is this room ? Is it in a residence or a hall ?

@Genieveve: this is a sort of partition between hall and guest/ living room

Thank you veejar:)
I would gilded with gold ,this place looks precious ,I can even visualize a mural painted on it , lets see if I can find an idea ,

Can you visualize trees painted on those columns and a blue sky like the one in the idea photo in this room? I can :)