advanced level, high grade, senior
Example sentences
上級者が英語力（特に読解力）をつけたければ、語彙を増やすのが王道ですね。
If the more advanced want to improve English ability (especially reading comprehension) increasing vocabulary is the way to go.
例えば、私は、来年進学する大学の単位が実際にもらえる数学の上級クラスにいます。
For example, I am in a high-level math class that actually gives me college credits for next year.