You can remove all constraints by selecting all tasks and clicking the Information button on the Task ribbon. Set the constraints to ASAP.

If you manually colored the table, you can reset the table back to Global.mpt default (default fonts, background colors, columns etc) through Task ribbon, click the Table drop-down and select Reset to Default. Actually I have to amend that - resetting does not removed manually applied background colors. Select the column or columns and set the background to none. It will remove all manually formatted background colors.