Like in title. I can’t change 128 to 320. It’s important because I need better quality (320). My system: Windows 7 Home Premium, Audacity 2.0.2, LAME 3.99.3. I read that I should go to Edit >> Settings - but i don’t have Settings! I’ve got Preferences only. But OK, it’s name only… I should find there ‘‘File formats’’ but nothing that’s not there. I give you my print screens. Thanks for help 
You may have been reading documentation for the old (obsolete) Audacity 1.2.x series.
In Audacity 2.x the MP3 settings are within the Export dialogue - click on the “Options” button.
(see here: Audacity Manual)
Once you have set the MP3 export settings those settings will remain unless you change them.