I don't know where the original responses went, but there are two issues here:

1. You release the backwires usually by inserting a small screwdriver in the rectangular hole next to the place the wire is inserted and pulling on the wire at the same time. Sometimes, it's easier to just cut the wire and start over.

2. If your wire is silver, you better investigate whether the wire is indeed aluminum. If so both the existing receptacle (with it's backwiring) and probably what you envision replacing it with (most dimmers have little pigtail wires on it which you can not just connect via common siring nuts) is a severe fire danger.

Look for writing on the outside of the plastic containing the wire, if you can't see that, scrape a little of the metal (power off at the breaker) to see if the wire is copper colored or silver (aluminum) before proceeding!

Thanks for your response to my ?. I am thinking that the house wire is indeed aluminum due to the color and the dimmer I have does not have any wiring ,only screws and holes for back wiring. So.....are you advising that if the house wiring is aluminum I should not add the dimmer and get help? Thanks again.