I have an image that I need to change so that it is print ready, it is going to be a large birthday banner. I have no experience with this and wondering if Adobe is the right platform for me to use?

I have an image that is based off of an invitation that I made for my sister's birthday party. I’d like to make a custom banner (8ft wide x 18 in high) but I can’t figure out how to make this image print quality. Any help would be appreciated. I am planning to use Vista Print for the banner. Thank you!