When overtype mode is enabled in Word 2010, it will start replacing the existing characters wile typing text before any other text. You can turn off this feature using the option provided as part of Advanced Options.
Step 1: Click the File menu then select Options.
Step 2: In the Options screen, click Advanced tab then navigate to Editing Options.
Step 3: Turn off the overtype mode by un marking the check box with caption as Use overtype mode.
Microsoft word also allows users to control the overtype mode with toggle switch using insert key. This can be enabled by marking the check box with label as Use the insert key control overtype mode.