Another possibility is a filter preventing you from seeing the manyu. That'd be a dropdown menu directly below the previously mentioned tabs.

To upgrade your units (use your manyus) you start by clicking on the Units tab.




You then click on the "Character Upgrade" tab and select the unit you want to upgrade.






Now you are at the upgrading screen and need to select what you want to use to upgrade.
You can use Manyus, Ampies, skill- and dressblooms, or even units themselves.
For now just worry about using manyus. To begin, click the first box (Don't worry, you can select all 10 manyus at once)




You may want to sort and set it so you only see what you care about (in this case manyus).
To do so, just select manyus only from the 2nd drop down list as so.




It is important that we match manyu type to the unit type. In this case we are upgrading a Hit unit.
You can tell this by the blue hammer icon in the top left corner of the unit.
Type matching will increase experience gain by 50%!!
Now there are 3 different types of manyus you need to distinguish if you want to be efficient.
Lv 5 manyus should be used on units lv. 1~35.
Lv 20 manyus should be used on units lv. 30~55.
Lv 100 manyus should be used on units lv. 48~80.



Always upgrade in groups of 10 manyus unless you are almost at the max level for your current evolution state.
Max Levels
Bronzes and Silvers: Base: 50 Evolved: 60
Golds and Rainbows: Base: 60 Evolved: 70 Bloomed: 80

Once you have selected 10 manyus of matching type it is time to upgrade!


Congratulations! Unit Upgraded!

Note that it's not necessary to have matching manuy type but it's still recommended. Using unmatching manyu will just give less Exp to your girl. So, sometimes, you may still want use every kind of manyu on a girl for some reasons.

yes but 50% increased efficiency can make a world of difference. I know it can be tough starting out as you want to be able to clear E-8, but you end up paying more in the long run.

Also if you do not need 10 to get to the level cap (5* 60 before evo 70 after etc) then only use what you need. No point wasting them.