Here's the tutorial...
First you’ll need to click on the Dimension and choose Dimension Style from the menu.
When the Dimension Style Manager dialog box is open, click on the New button to display the Create New Dimension Style dialog box.
Type a Style Name in the text box (for example: New Dimension Style ) , choose a dimension type from the drop down list and click on the Continue button.
As an option, you can check the Annotative Check Box to make the new dimension style annotative.
On the Lines Tab you can set the options for Dimension lines (color, linetype, lineweight, etc.) and for Extension lines.
On the Symbols and Arrows Tab you can choose the Arrow Heads, set the Arrow size and setting other few fields.
On the Text Tab, you can set the Text appearance (text color, fill color, text height, etc.), the Text placement (settings for vertical and horizontal placement) and the Text alignment.
On the Fit Tab you can choose an option from the radio buttons list and set an option for the Text placement.
On the Primary Units Tab you can set the units for Linear dimensions (unit format, precision, scale factor, etc.) and for Angular dimensions.
On the Alternate Units Tab you can set the options for Alternate units (unit format, precision, etc.) and the Placement.
On the Tolerances Tab you can set the Tolerance format (method, precision, etc.) and the Alternate unit tolerance.
And here’s the result after a new dimension style was created!