Total Commander

So that we don't need to select and delete them one by one.

Duplicates of what? You can have two files with the same name in the same directory, anyway...

Duplicates are files with same size and contents.

I think it wouldn't be too hard to compare by date/size, but by contents is a bit more difficult.. you would have to read the entire contents of every file (one way or another). It can be optimized by calculating a CRC or fuzzy code of some sort, but still... I think it goes a little beyond TC's scope.

Why not use a program like Unique Filer?

Yes but with a, so vital, warning message. It's still not safe but there are cases where you can save time with an automated selection of the duplicates. You can then start to exclude selected items which may be a lot fewer than having to select the needed ones.

Performing the duplicate search in a specific location and further down the dir tree can be even safer. But this is a wish for speed and the implications are well known to everyone.

A warning message please... and maybe a two-stage verification would be even better and safer!