basically, you login as user dietpi. Means this user need to have r/w permission on the files you like to adjust/edit/delete. Have a look to the directory in question and check who is owning them. At the end it comes down to user permission on file system level.
If you don’t mind and security is not an issue, you could switch Samba login user to root. This way you bypass security issues. Or you change to SCP instead of Samba. There you could use root user as well.