Before you install or upgrade MyBB, you need to download it to your computer. The latest version of MyBB can always be found on the MyBB Official Website. The release can be downloaded in either ZIP or GZIP format for people using different operating systems. The download is just over 1 MB and should take no more than 4-5 minutes on a Dial Up connection.
Once you have downloaded the file, it's time to unzip it. Using an archive utility capable of decompressing the download format (eg: Winzip), unzip it to a location where you can access the files shortly (perhaps the desktop?). After that, you can proceed to install or upgrade.