If you mean maximum legal enchantment levels, such as Sharpness 5, Protection 4, Fire Aspect 2, etc., you can do that with an anvil using the item you want to enchant and an enchanted book obtained in Creative Mode (all enchanted books in creative are max level).
You can also use
/enchant <player> <enchantment ID> [level] where
<player> would be yourself,
<enchantment ID> would be the numerical ID of the enchantment, and
[level] would be the maximum level of that enchantment. This command applies the specified enchantment to the item in your hand. You can find a list of numerical IDs and levels here.
However, if you're hoping for enchantment levels higher than the maximum legal ones, such as Sharpness 2000 or Protection 10000, you'll need an NBT editor such as NBTExplorer to change the enchantment level through the world data. You can also use Essentials on a server, but that solution leaves the vanilla scope and is less efficient for a simple enchanting task.