Aww! You love it? Thank you♥

Not a noob question at all. Here're some instructions:

1) You go to your Journal > Journal style
2) There you can search for a theme, right? You type Flexible Squares. On the first page you see a theme named "Greys" and under it you can read "Flexible squares by Yati Mansor." Apply this theme.
3) Then go to Cuztomize your theme(Where tranquil_ity's current theme is written)
4) There you go to Custom CSS (Under Display, Bar and etc.)
5) You'll see a big quare/rectangle(Not the small one )
6) There you'll place this code:

.headerimage {
height: 760px;
background-image: url("http://i306.photobucket.com/albums/nn245/pamsblau/Wonderfulmess-1.png") !important;
background-repeat: no-repeat !important;
background-attachment: scroll !important;
background-position: center !important;

7) Save changes(Under the big square) and you're ready!

If you have any problems, just tell me. :)