To get a level 10 item, you will need to level your items via the process explained in the MOD 0 achievement. In order to level an item multiple times, you will need to have more Happy Stars and more items to use as materials per level up. It is best to go for this achievement on an item that is not a premium item. The reason for this is because eventually, you will need to level up other items that you are using as materials to level up the premium item. If you are leveling up a non-preminum item, you will not have to do this.
There is now also a Material Points Up buff in the game that may be found on any type of item present in the game. If an item has this buff, it will give more material points when you use it to level up another item. The extra material points depend on the level of the buff and are as follows:
Material Points Up Lvl 1: 100 more material points
Material Points Up Lvl 2: 300 more material points
Material Points Up Lvl 3: 600 more material points
Please see MOD 0 achievement description for more information.