Summarize the following:
If you have two enchantment books with the exact same enchantment and level, you can combine them in an anvil to create a higher-level enchantment.  Combining two level I enchantments yields a level II enchantment (if applicable). Combining two level II enchantments yields a level III enchantment (if applicable). Combining two level III enchantments yields a level IV enchantment (if applicable). Combining two level IV enchantments yields a level V enchantment (if applicable). For example, if you have two "Power III" enchantments, you can combine them to create one "Power IV" enchantment. You cannot combine enchantments of different levels (e.g., "Power I" and "Power II"). Select the anvil to open it. Select one book and select a box on the left side of the anvil, then select the second book and select the other box on the left side of the anvil. You'll see a new book appear on the right side of the anvil's window. Select the book, then select your inventory.  On Minecraft PE, tapping the book will move it to your inventory. On consoles, select the book and press Y or triangle. . If your combined book isn't the highest attainable level for the selected attachment, you'll need to create another version of the book in the enchanting table and then combine it with the current combined book. You'll repeat this process until you get your enchanted book to the highest possible level.

Summary:
Understand how combining enchantments works. Make sure that you have two of one type of enchantment. Open the anvil. Place both enchantment books in the anvil. Move the combined book into your inventory. Create another enchantment book