Newbye here, so sorry for stupid question.

I don't know how to use different skin for my V8.

I have uploaded some JPG files into data/skins folder but they don't appear on LFS menu.

Any suggestions?

Open LFS.
Goto the garage.
Make a new Colour set (theres a "new" button under the gird of colours on the left).
Now on the "info" button you can select a skin. Your skin will be in this list.