how to change the toobar icon

hello everyone, recently my boss give a task , to run the autopsy and change the icon of the toolbar.
I download the autopsy-X.X.X-64bit.msi and install on my computer.
After installed I found tho icons are in the org-sleuthkit-autopsy-core.jar , so there I change it ,but it doesn’t work on the ui.
Is there anyone could tell me what wrong with it , and how can I replace the icons.