0ce40265_Class___CodeIgniter_User_Guide__Description
[Preference] overwrite [Default Value] FALSE [Options] TRUE/FALSE (boolean) [Description] 
If set to true, if a file with the same name as the one you are uploading exists, it will be overwritten. If set to false, a number will be appended to the filename if another with the same name exists.
File Uploading Class : CodeIgniter User Guide
Description