How do you convert alto sax notes to tenor sax notes?
If you are writing in longhand, add a flat or remove a sharp from the key signature, then move all the notes up a perfect fourth (or, you could analyze the scale tones from the original key, then write out the corresponding scale tones in the new key). If you have access to some notational software, most are capable of transposition. I’m a big fan of Finale products (I tried Sibelius, but find Finale more practical to use), and all of them are capable of transposing any selected passages to another key or within the existing key. Go to www.makemusic.com if this sounds like something you might pursue; the entry level program is only $9.95 and is adequate for some work (as well as a simple version to learn). If you find it inadequate in due time as I did, wait for them to bait the hook with upgrade deals at a discount.