bullet points in word keep changing format

Two things cause this. Word's AutoFormat turns lines starting with * or - into its own bullets, and pasting in text from somewhere else drags that text's list style with it. For the first: File > Options > Proofing > AutoCorrect Options > AutoFormat As You Type, untick Automatic bulleted lists. For the second, paste with Keep Text Only (the clipboard icon that pops up after pasting, or Ctrl+Shift+V in newer versions). Then apply bullets with the List Bullet style from the Styles pane instead of the button. That way every list in the doc uses the same definition and they stop drifting apart.