how can i tell if a song is an mp3,4 or lossless in iTunes

Are you going to rerip these from CD?

If displaying columns you can choose the option to show "kind", or you can look at the summary information for a track in Get Info.

Note, saving a file to a higher format will not increase quality. If anything you risk losing more quality. The only way to get lossless quality is to re-rip your CDs or find a vendor who sells lossless files (Apple does not)..

You can use Smart Playlists to filter your library against any combination of Kind - using values:

• "AAC audio file" for AAC / M4A (via CD import or conversion)
• "Purchased AAC audio file" for Store purchases
• "MPEG audio file" for MP3
• "Apple Lossless audio file" for ALAC
• etc

and Bit Rate. For example, this:

will show all MP3 files whose bit rate is less than 256kpbs. This (for my library, at least) will show everything that is not lossless:

As Chris hints, the only way to "upgrade" media to lossless is to re-import it from CD or from lossless files. Converting from AAC or MP3 to ALAC or AIFF will just give bigger files with no improvement to audio.