1. Go to any List Edit screen (e.g. IE05 or IH08).
2. Click on a field that has drop-down list (e.g. Technical Object Type) and click the drop down button.
3. Point the cursor on some area inside the newly opened list and right-click.
4. Click on the "Personalize" option.
5. You have 2 options: To set defaults only for this particular field's drop down list (Settings current F4 helps) or to all (Settings for all F4 helps), click your choice's appropriate tab (for this example I am choosing the second option (Settings for all F4 helps).
6. Make the necessary change you require in the "Max. number of hits to be displayed" and/or "Maximum width of hit list (in chars)".
7. Click on the "Copy initial system setting" button.
8. Click the Enter button (the green check mark).
That's it. I hope this was useful to you.