The meaning is more or less the same, but the usage would be different. The first sentence, with the word "by," sounds condescending, and might be used when speaking to a child or to someone you consider lacking in intelligence. If said to someone who is your intellectual equal, it would sound insulting.
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AnonymousYou could learn this yourself.= You yourself could learn this.
AnonymousYou could learn this by yourself.= You could learn this without any help from others.