How to change icons

this might look like a pretty stupid kuestion...but ha...i really dont know how to change a set of icons...for example, change all my icons to DopusXp (Cris van Minnen, *.icl), i could find any topics on this...
sorry if it is already posted...

Unless the creator of the icon pack has provided an Opus toolbar file, I'm afraid you have to edit each button on your toolbar and change the icons individually.

Opus doesn't currently have the concept of interchangeable icon sets and the icon for each toolbar button is completely independent of the icon for any other toolbar button. (Which is good sometimes, but not so good if you want to swap one set of buttons for another.)

it has this in the description
XP-like Toolbar icons for Directory Opus 8 with Alpha Channel
...being a toolbar how can i install it?

There is nothing to install. Just unzip the DopusXP.icl file from the zipfile and put it anywhere you want.

Then put DOpus in customize mode, edit the toolbar button you want to change the icon of, then click the button that says "1".

Next tick the option that says "Select image from a file",
Then press the button on the right that has an open folder on it to browse to where you put the DopusXP.icl file and select it.

In the preview section you should then see all the icons in that DopusXP.icl file. Just pick the icon you want to use with your button.