1) Download your blog template contents as a backup. That way if you screw something up and need to go back to the original, it's no problem. If you host on BlogSpot, I have no idea how to do this... If you host on your website like I do, just login to your FTP server and download the whole blog folder with the contents inside.
2) Login to your blogger account, and go to Template Tab > Edit HTML.
3) There are 3 numbers that I changed. First one was the "header" pixels. I changed this from 660px to 800px. If you want your header (sometimes called banner) to be wider then make the number even larger, or of course smaller if you want it smaller. If you want your header to stay the same as it already is, leave this number unchanged.
Screenshot to help you locate #1:
The second number I changed was the "content" pixels. I changed this from 660px to 1,000px. I think this number is the width of the entire blog (the content AND the sidebar).
The third number I changed is the "main" pixels. I think this is the width of the main section of the blog, where your type and photos go (not including the sidebar). As you can see, I'm no pro at this, but it worked for me!
Screenshot to help you locate #2 and #3:
4) Once you have these numbers changed, you can click the preview button and see how it looks. If it the width looks good, then save the changes and republish the blog. There should be buttons to click for all those.
5) Now it's time to upload your photos. As far as I know, you *cannot* use bloggers photo uploader to upload your photos, because it limits the size to the default size. If you do use it, your blog will be supersized but the photos will still be small. So, you need to size your photos (photoshop or whatever image editing software you use) to the actual size you want them displayed on the blog. Mine are 700 pixels on the long side. When you get your jpeg file sized and ready to go, you need to put it on the internet somewhere (FTP to your own website, flickr, photobucket, etc) and get the link for your image.
6) This is the code that you will paste into your blog post- Click here to see it (blogger tries to display the image if I paste it here)
Thats it! When you get the code in there for the images, then publish the post just as you would normally, and of course check it out to make sure it looks good.
If you have questions, leave a comment with your question and I'll do my best to help... but I am no pro at this... so beware. And, everyone's blogs are different, so try not to ask questions like "Where is my code for the header?" because it could be called a totally different thing on your blog and located in a totally different place, so I couldn't really help you out with that.