Hi!
Pls, can anyone tell me, how to correctly change logo in viart shop? My default template is ecommerce black. As default the shop loads logo from /images/logo.png. But ITS WHITE! And my template is black. In black oscommerce template loads black logo! I want to customize logo so, that it will look like so was.To make so that it was not visible edges. How to do it and what file I should customize? There are many logo files.

When you're loading a logo, you need to have a .png logo or a .gif logo so that it doesn't show the white areas. With those file types, the white area is made transparent.
 
I'm assuming it's your logo file, but I could be wrong.

So, then the best idea is to use print screen to create an image file with 150x55 parameters and same colors

possibly, but I'm not sure what your site looks like. Or you can modify your logo using photoshop and this will fix what you need.