Deleted files stay in backup location

[Sphinxx89]

Hey Guys,

I've run into a problem. But first let me explain my setup. I use Sync to do backups of my phone (Galaxy S7 Edge) to my NAS (Synology DS216J).

Now the problem is when I delete files from folders that are synchronized they are not removed from my NAS.
I think the problem here is the folder permissions. When I go into the browser to manage my folders it says this when I hover with my mouse over the folders:

/volume1/myname/backup/
read only - standard folder

Now I kinda assume that the "read only" parameter needs to be changed to "read/write" but I can't seem to figure out how. Permissions for my and my admin account are all set to read/write so I dont now where to change this.

Any help?

 

[Helen]

This is how backup from mobiles work: 
if you delete files from a mobile, after they are backed up to a desktop, this deletion is not propagated to desktop. 
if you delete files from a desktop, after they are backed up from mobile, this deletion is not propagated to mobile, because desktop is Read-only peer. 

There is no way to change desktop here from Read-Only to Read-Write, because this is how backup works - it shares only RO link/key with others.