You simply have to sand them to remove the finish, then apply your chosen stain or paint.

Minwax makes a product that lets you re-stain without stripping or sanding.

It's called Polyshades, and I've seen it at Home Depot although I've never tried it. I've osed other Moinwax finishes though, and their stuff is generally really good.

http://www.minwax.com/products/onestep/Polyshades-color.cfm

I am staining my own kitchen cabinets right now! Mine started out darker than yours, but I think the process is the same. I removed the doors and all the hardware, and starting with the doors, did 2 passes with a mouse hand-sander - the first with 90 grit to get the old finish off, and the second with a fine grit 150 for a smooth surface.

I am also using a minwax product, but I choose the Woodsheen: http://www.minwax.com/products/onestep/woodsheen.cfm because it is a gel, easy to work with, and so far is giving me very professional looking results. I am just wiping it on with a cotton cloth, very thin, and doing 3 coats. This stuff has the topcoat in it, so once the last coat dries, the cabinets are done. I did the doors first, and am now working on the wall mounted frames, and then will reinstall the doors with new nickel hardware - my old hardware is not as lovely as yours is!

So far, my big lessons learned are, stain the doors on a flat surface, so that the stain doesn't pool in the corners of the detail work on the front, and that the job is coming in at the right cost, but the time factor is about 3x what I initially anticipated. But....everybody who has seen the work thinks it was done professionally, so thank you, minwax!

Kenn, I actually have used the Minwax Polyshades product that Keith mentioned to achieve the exact same effect on my kitchen cabinets. Both Lowes and Home Depot carry it here where I live. The only problem is there are very limited hues available. I used Bombay Mahogany in a satin finish (it also comes in glossy). Three coats gave me the desired ebony finish. 1 and 2 coats, it comes out looking very reddish. Only a light sanding before application, to rough up the finish for better adhesion, is required with a light once over with steel wool between applications. MUCH easier than sanding and removing the old finish. I did mine 2 years ago and they're holding up great. I don't have any photos on Flickr or anything, but let me know if you'd like me to send you a photo of my end result.

Thank you for the advice, all. I am amazed and pleased that I won't have to completely strip the wood of the current finish to obtain the new finish. Looks like Minwax and I are going to get REAL acquainted :)