Can I change the type in this menu to Uppercase letters?

You can use the text-transform CSS property to change fonts to uppercase. See http://www.w3.org/wiki/CSS/Properties/text-transform

Here is an example of using it for the main menu of the Oxygen theme:

.main-navigation ul li a {
	text-transform: uppercase;
}

.main-navigation ul li a {
   color:#000;
}
.main-navigation ul li a:hover {
   color:#fff;
}
.main-navigation ul li a.active,
.main-navigation ul li a.active:hover {
   color:#fff;
}

You can change out the color codes to adjust it.
http://0to255.com/

put the menu in tabs?

For this one, I would recommend searching for a tutorial until you find one you like and then adjusting the CSS selectors until you get the effect you want. I searched and found one possible example:
http://matthewjamestaylor.com/blog/beautiful-css-centered-menus-no-hacks-full-cross-browser-support

Their example menu uses an ID "#centeredmenu" for the base menu selector, but the Oxygen theme uses a class ".main-navigation" so you can just swap that out to make it work:

.main-navigation {
   float:left;
   width:100%;
   background:#fff;
   border-bottom:4px solid #000;
   overflow:hidden;
   position:relative;
}
.main-navigation ul {
   clear:left;
   float:left;
   list-style:none;
   margin:0;
   padding:0;
   position:relative;
   left:50%;
   text-align:center;
}
.main-navigation ul li {
   display:block;
   float:left;
   list-style:none;
   margin:0;
   padding:0;
   position:relative;
   right:50%;
}
.main-navigation ul li a {
   display:block;
   margin:0 0 0 1px;
   padding:3px 10px;
   background:#ddd;
   color:#000;
   text-decoration:none;
   line-height:1.3em;
}
.main-navigation ul li a:hover {
   background:#369;
   color:#fff;
}
.main-navigation ul li a.active,
.main-navigation ul li a.active:hover {
   color:#fff;
   background:#000;
   font-weight:bold;
}

You can also adjust all of the colors and spacing values in the example if you'd like.
http://0to255.com/

At the top Primary menu bar- is there a way to give the menu a background color?

Here is an example showing how to change the background color and add padding to the the main menu in the Oxygen theme:

.main-navigation {
	background: #f7fd67;
}

.main-navigation ul {
	padding: .8em 0 0 1.5em;
}

You can pick a different color code and change the padding numbers to adjust how it looks.
http://0to255.com/

I am new to WP, and am using the Oxygen theme to set up a site. I need some help with a few things and would appreciate your help in any way!

1. At the top Primary menu bar- is there a way to give the menu a background color? put the menu in tabs? and change the font color?

2. Can I change the type in this menu to Uppercase letters?

Thank you very much for your help.

The blog I need help with is otiumdesignandfineart.com.