All hinges are "demountable."
Conventional hinges are available in two configurations, flush overlay and inset. Changing to a hidden hinge requires patching of the screw holes.
Which type do you presently have?

This is what I have.
there is a T slot in the base of the cabinet ad and a slot in
the side of the door
No screws into the face of the cabinet.
Has anyone converted from this style to a concealed hinge

Double Demountable 1/2" Overlay Hinge

Your next step is to select a hinge you want to install.

As a simple explanation, lets say BLUM, as a for-instance.
There are two choices; 1. Relocate the hinges, remove the doors and have the doors drilled and prepped by a local cabinet shop, purchase the frame jig, drill the face frames and set the hinges. 2. Plug the doors and face frame and proceed as in #1.

Thanks. I'll call around. I have a lot of doors. May be pretty expensive

The doors are not partially recessed, right? (if they are, you need to id that when you replace the hinges.

With the doors closed, what is the overlay measurement (sideways)? Looks like 3/4" or 1" maybe? Once you have determined that, you want to buy hinges with the same overlay (and other dimension, if they are recessed). If you're not a novice, you can buy a forstner bit and bore the holes yourself (carefully). Or you can remove the doors (mark and number them with tape), then take them to cabinet shop (call first to arrange this, or call a hardwood supplier and ask for a reference) and have them bore the holes for you (not a bad idea, btw).

Then install the hinges on the doors. Finally, install the doors to the frames. Pre-drill all holes.

the doors are overlay , 1/2 inch

Demountable hinges come in unique style of single and double varieties that mounts on the cabinet or door. The best thing which I really like about this type of demountable hinges on the door is the convenience they offer. One can easily remove the cabinet door from the cabinet frame and can move to their convenience.

Here is a link that might be useful: brass hinges

I have some double demountable hinges that no longer hold the door tightly. If you have any suggestions or experience with this problem pls post a reply. Thank You.

Here is a link that might be useful: A few Hinge pictures

Did you end up changing these to concealed hinges? I have the single demountable hinges and want to update the look of the kitchen as well. I was wondering if it's worth the cost/work. I have about 60 hinges to change.