I’ve setup an account, and download Yahoo! Messenger 8.1. But i can’t login with my account, and the website says the installer is not patched, but it doesn’t say how to patch.
Note that you are expected to have reading comprehension. We’re not going to hold your hand through every step. We do not provide help with manual patching - you should only do it if you know what you’re doing and can understand what is written on the page.
Anyhow, follow this section in the patching guide.