How to Upgrade Disks in ReadyNAS Duo V1

Thanks AGAIN, StephenB and vandermerwe!
One more question at the bottom, please!

I tested my UPS by setting my ReadyNAS setting to auto-shutdown at 90% and pulling the plug.

That seemed work a-okay.

After plugging the UPS back in to utility power, I did a normal power on/boot up on my ReadyNAS,
and the UPS monitor display showed 85% on the UPS battery and a more reasonable 64 minutes.

After the UPS battery got mostly recharged up, I changed the auto-shutdown setting to 40%
and successfully operated the the ReadyNas for about 5 minutes on the UPS only power.
It only declined to about 75% on the UPS. Then I plugged it back in.

Here's my final question:
I have two windows PCs and they are setup with screen saver user IDs and passwords.
I would like for only those two users to be able to delete and/or rename files and folders within my media share.
Casual users, like visitors and even us on other devices like smart phones and iPad, should only be able to READ files, view pictures, play video clips.

Can you tell me how to do that? And will your permission settings apply to streaming services like DLNA or iTunes server?

Thanks so much, I'm sorry to be such a dummy at understanding LINUX security.
I assumed that the ReadyNAS Frontview would be a user friendly interface to setting the share/folder/file permissions?

Thanks, Bob Nesiba