SSMS Backup databse

I use SSMS to back my database and realized that SSMS add newer database to the same file.

For example, I use MyDB.bak file to backup my db.

I look the content it inlcudes all previous version of the date of database.

I would like to backup up to one week.

Can you please advise how to configure SSMS to back database  for lat 7 days?

Your help and information is great appreciated,

Regards,

Souris,