Stuff that F2Pers don't get
Less bag and character slots
Map wide chat
They can only whisper every 30 seconds
They can't join WvW(the server v server v server pvp) until they're level 60
They can access the Trading Post but can't mail items to other players.
Anything in the Heart of Thorns expansion
To upgrade they need to buy the expansion, which will give them three character slots, more bag slots on every character, access to the Heart of Thorns content such as new maps, guild halls, raids, elite specializations and a new class.