How to update antique furniture?

First you must sand off the stain that is on the piece, as well as any topcoat (such as varnish) that might be on the piece. However light it is now is the lightest color you can get. Now you can apply your stain. Make sure you use an older type of topcoat such as varnish, shellac, boiled linseed oil, tung oil, etc.

It will most certainly devalue the piece. If it is a valuable item, worth a significant amount of money, I would advise against it. Before making any decisions, have the piece or pieces appraised by qualified dealer that belongs to a recognized society.

Any DYI to it will ruin the value of the antique. Absolutely, no doubt about it. Even professional restoration where the item looks "new again" can ruin the value of an antique - as several people learned over the years on Antiques Roadshow. They had items that if left alone would've been worth 6 figures reduced to a couple hundred dollars because of DYI or restoration work. The question then is can you afford to "eat the loss"?

If it is a an old piece that was 1.) mass produced and 2.)there are still gobs on the open market left available and 3.) you have no financial investment and 4.) an appraiser doesn't value it more than $200 to $500, then have a ball and do what you want.

Thanks for the great advice! I will definitely investigate further before doing anything.