Google Chrome allows you to change the browser default search provider at any time. Click on the wrench icon in the upper right corner of the the Google Chrome browser and then click on "Settings" from the drop down menu. In the Settings window, use the drop down menu in the 'Search' section of the page to select your desired search provider.
Note, if you are seeing Ask.com whenever you open a new tab, you will need to uninstall the extension responsible for this. Instructions for removing our extension can be found here: http://support.mindspark.com/ics/support/kbanswer.asp?questionID=223