Masks

You have the problem that many of the brightness tones (and colors) of the necklace are the same as the background, so all 'auto' methods to isolate the beads are prone to failure.

I think you have two choices-

1) Reshoot the articles on a dark (black?) background.

2) Manually 'paint' the article with a Brush (in the Masking tools) and adjust-

Try Select Subject in the Masking list. Sorry, just tried it and it doesn't work well with this subject.

I have uploaded a photo twice and it keeps disapearing.  I am not sure what I am doing wrong. I will try this again.

Another idea is to use a gradient mask.

Create a gradient mask outside your picture so that the whole picture is affected. The subtracted the appropriate area with the brush tool.

Show us one of your images.

In general, if the background is one color and the necklace is another color, you can use the Color Range mask to select the background, but not the necklace, and then lighten the selected background.