I would like to help you get through this process. I think it would be best to take it just one part at a time, when you get through that part you can go onto the next. The first thing you should do after downloading the new PowerCMS is rename the downloaded folder to the name that you want to have for your cms folder in your site. You then need to upload the files to your server.
Once you have done that you will need to browse to the folder that you just uploaded to your server. When you do you will start the installation process. Once this process is out of the way you will be able to add content to your site through the CMS admin area.
Please go through with uploading the files and getting through the install so we can start on the next part. If you have any trouble with any part of this post back with some info about what you are doing and what the result is.