how to erase a variable

[greenflame]

Is there a way to get rid of a variable as though it never existed? I
know this sounds very basic but I have not come across any such
methods. Also is the fact that I will have a bunch of extra variables
just haning around because my use for them is over a bad thing? I will
likely have on the order of 10 to 50 or so of these for the particular
program I an working on at the moment.