There are too many differences to list. In the LN, the author pokes fun at his own mistakes he did in the WN and frankly it's weird to read the WN after reading the LN, so I recommend you start with the WN from start to finish and then change to the LN since the LN is different enough that it doesn't feel like reading the same story again, aside from maybe the first 2 volumes, but from LN vol. 3 on it starts diverging more and more, though the general outline of the story is still more or less the same. Though I heard in later untranslated volumes it changes so much that it's basically an entirely new story that can never reconnect with the WN again.