Always use true numbered (ordered) and/or bulleted (unordered) lists. (Never use “lists” created by tabbing with images, etc.)
For Bullets: Go to Home > Paragraph area of the Home ribbon > Bullets.
For Numbering: Go to Home > Paragraph area of the Home ribbon > Numbering.
To add a sub-level to the list, just click Tab to indent or use the Increase Indent option: Go to Home > Paragraph > Increase Indent.
To go back a sub-level, just press Shift + Tab and it will move your list item back a level. Or, use the Decrease Indent option: Go to Home > Paragraph > Decrease Indent. You may also use the Change List Level option found in the Bullets or Numbering options. If you have a new list which won’t automatically restarting numbering, right click on the errant number/letter/Roman numeral and choose the Restart option.
Note: If lists are giving you grief, remember you have the option to Clear Formatting. (The icon looks like an “A” with an eraser in front of it.) This is found in the Font area as well as the Style Ribbon of the Home Ribbon Tab.