Hi kgobin,
Please, follow these instruction to solve your problem.
1. Login to your WordPress dashboard, Go to Appearance > Editor (It is enabled by default)
2. On the top-right hand corner, you’ll find select theme to edit.
3. Choose your active theme from the list , and click select. (To figure your active theme, just click appearance. First in list with active: before theme name is your active theme like Active: Twenty Ten. Then, follow the procedure)
4. On the right hand side, there is a sidebar which contain template along their file name underneath. Then, you’ll see styles under that template list.
5. Click Stylesheet (style.css), when It is loaded at the end of file/stylesheet add following lines
.blog-post img {
border: none;
}
Now, Go to Settings > Permalinks and click Save Change.
And, you are good to go.