Hi Duurduur,
In order to reduce the "Voice Wave Size" (= required storage space for all wave samples of the Expansion voices to be installed), click on your "Install Target" in YEM, i.e. your keyboard model, and then deselect voices that are not required so that the green tick in the relevant voice icon disappears.
"Keys" icon means Normal Voice, "Drum" icon means Drum Voice, see also attached screenshot.
Note: Deselecting other file types (e.g. Styles, Multi Pads, Registrations, MIDI songs) in Expansion Packs does NOT reduce the "Voice Wave Size" since these other files are not stored in the Expansion Memory but in the USER Memory (there in the "Expansion" folder).
Hope this helps!
Best regards,
Chris
[attachment deleted by admin]