What's incremental backup type? Will incremental backup type every days replace the old backups from previous days?

Incremental backs up all changed files and then marks the archive bit off. Meaning... if you have a full backup, you will need incremental tapes for every time you back up. If i back up on Monday a full backup and then on Tuesday and Wednesday i do an incremental backup, when i go to restore i would need to use the full backup, then Tuesday, and then Wednesday's backups to get all the data back.

So that means i need 2 or more external hard drive? Why is not a good way just choose Differential Backup then?

No, if you are using an external hard drive, just change the file names.

So is no very convinience each time i have to manually change the backup file name. I mean backing up on the same hard drive with incremental backup type daily i need to change the backup file name?