Editing numbering styles

WP 12 : So what, please, is the special secret to be able to edit numbering styles; attempting to follow the "Help" details proves fruitless. Specifically, when I choose the first style option shown in Outline/Bullets & Numbering (1. a. i. etc.), its preview nicely shows that the second level (a.) is indented as it should be. When moving to that level in text, however, it is remains lined up at the left margin with 1. (even though i. (1) and all the rest are at their proper indents). In an earlier rendition of WP I was used to, I could go into edit, into the reveal codes box there, and insert a HdLeftTab or LeftTab or whatever I needed to correct the problem; with WP12, however, after making that edit there is no OK button available (grayed out), so all I get for that bit of effort is to back out by Cancel .... and the second level a. remains stubbornly where it wants to be.

Any suggestions?

Much appreciated.