I believe that there is Xyz monsters that consist of ranks and Monsters with levels. There are some cards out there that state that you can change the level of a monster on the field (such as raise the level of a monster by n). Can I do this on Xyz monsters?
An Xyz Monster's Rank is not its Level; Xyz Monsters do not have a Level. Consequently, Xyz Monsters cannot be used for Synchro, Ritual, or Xyz Summons (unless specifically permitted); and any effects that would refer to the Level of a monster, such as those of "Gravity Bind", "Level Limit - Area B" and "Burden of the Mighty", cannot be applied to an Xyz Monster. Since Xyz Monsters do not have Levels, cards such as "Star Changer", "Scanner" and "Give and Take" cannot be used on them at all. Cards that modify Levels such as "Harmonic Waves", "Feedback Warrior", "Synchro Boost" and "Demotion" also cannot be used on Xyz Monsters.
You can only use effects that change Level on monsters with a Level, and you can only use effects that change Rank on monsters with a Rank; you can't use ones that require a Rank on monsters with a Level (or vice versa), and you can't use either on monsters with a Link Number.
Xiangsheng Magician is an example of a card that can change a monster's Rank; she targets an Xyz Monster and a Lv.5+ monster, both on your side of the field, and makes the Xyz Monster's Rank become equal to the other monster's Level. As of now (May 24, 2017), she's the only TCG/OCG card that can change a monster's Rank. [If playing by anime rules, she instead changes a monster's level, and her counterpart Xiangke Magician gives Xyz Monsters a Level equal to their rank. Needless to say, TCG/OCG Xiangke Magician has a nerfed version of this effect; he only gives Xyz Monsters a Level when used as a material for an Xyz Summon. Other cards that give Xyz Monsters Levels can be found here.]