Harddisk exchange / expansion

Hi all!

I own a 2110v2 ReadyNas with two 1TB Seagates installed. One of those Harddisks has increasing SMART-Errors for quite some some weeks, so I understand, it's time for a replacement.
I understand that the v2 can handle up to 3TB for each disk.

So I think, I will install new 2TB disks, which will be sufficient for some time.

My question. Can I just replace the increasingly faulty 1TB Seagate with a new 2TB disk? Will the new one be formatted correctly and the data from the other disk will be mirrored?
And after this activity I just replace the 2nd disk as well? Is is as easy as it sounds? Or do I need to adhere to processes that I might not be aware of?

And by the way: What do you think is the best and as well cheapest 2TB disk you could recommend?

Thanks for all hints and information!