Do you want to change where on the axes the tick labels are placed (no longer have labels at x = 1, x = 2, x = 3) or do you just want to change the label (have the text "10" at x = 1, etc.)?
For the former, use xticks as madhan ravi suggested or (if you're using a release that predates the introduction of the xticks function) set the XTick property of the axes.
For the latter, use the xticklabels function or set the XTickLabels property of the axes.
