Good lord. Lots of money buying and selling lathes just to lower yours.
Are the the legs steel or cast iron? If steel, have a welding shop do cutting and rewelding to shorten. if cast iron, have welding fab shop make replacements from heavy steel.
Is your shop location a permanent home with no expected changes or desires to get out of turning? If so, you could cut the concrete just to the size of the two legs and lower the lathe. Would need to lower and pour new concrete but may be cheaper option still.
Another idea is to make concrete forms to replace your legs. Pour two posts to your liking and imbed threaded rod into it. Cap with a steel plate if needed.
I would try try all options before the hassle of selling and buy again. Possible money loss and lots of hassle dealing with all the moving unless you just want a new lathe for some reason.
Good luck.