No change of the forum after changing the "Frontend" directory

Hi,
Newbie question again...
No matter what changes I made to the "Frontend" directory or any other files other than the "testforum" directory, the forum does not change at all...
In the "testforum" directory, however, there seems to be nothing that can be changed(no css, no js...).
So any tips?
Thank you!

Very helpful!
Appreciate it!