How do I make images bigger?

ok…. I need some simple code help please.
I am new to web programming.. had some programming way back in college.
I have been readding HTML XHTML, & CSS for Dummies.

The original programmer used Sliding doors theme.
you can see the pic of food plates on the main page.
I need to make it bigger:
https://www.mangosnoodlehouse.com/

pic is (actual) 900×675 .. I need it to be 1200×900 on the page.

current code puts the image ..centered on the page:
<img src=”https://mangosnoodlehouse.com/img/Food Photos/foodgrouping900.jpg” alt= “Great food at Noodle House.” />

I try:
<img src=”https://mangosnoodlehouse.com/img/Food Photos/foodgrouping900.jpg” height= “900” width= “1200” alt= “Great food at Mango’s Noodle House.” />
I get a higher height… but the width stays the same. so the pic is stretched vertically.

I tried linking a bigger image (1333×1000)… it looks small as the original.

I dont think it is margins, because you can see the heading “Come join us today… taste great traditional Asian Cuisine.” is wider.
what am I doing wrong???

2nd option:
How do I make that image sit on the Left of the screen.. leaving the center or menu and other items?

Thanks
Dan