世の中 means “world”. You might know “世界” which also means “world” but 世界 is often used as the physical world whereas 世の中 is “a world” with a concept of “society” or “era”.
“に (towards) 不満 (dissatisfaction) がある (there is)” following a noun, means “have dissatisfaction towards something” or “have a problem with something”.
なら means “if” or “given” which is used when the speaker sees or hears a particular thing or situation from the listener and explains what to do under the given condition. So Motoko hears the guy complaining about the current system and she tells him what to do under the condition which is that he’s got a problem with the world.
自分 means “oneself” so in this context it means “yourself”.
を is the particle which is used to indicate the direct object of the following verb.
変えろ is the imperative form of 変える meaning “change something”. So Motoko is telling the guy to change himself. Please note that if you use imperative forms in real conversations, it sounds really bossy.