Despite me starting to explain to you the much more complicated way of converting stuff manually using AVIsyth, I found this here tool which does it all automatically! It's called
Videora. Or you can just go
straight to the download page.
During install, it'll ask if you want to load it on startup. I'm not sure why anyone would, so I unchecked that. But anyhoo, once you got it runnin, you should prolly go to the Setup section first, and in the Settings tab, change the "Output Videos To" directory so you'll know where the heck it put it.
To actually convert, just go to the convert section, and you should be able to pick "One-click Transcode" to pick the file to convert, and it'll do the rest. If for whatever reason you want to adjust the bitrate and such, use the normal "Transcode New Video" button.
Andddd, that oughta do it.