Storage spaces, replace HDD or move data between physical disks, not possible?

I am sorry if this has been answered before, but there seems to be difficult to find enough information about Storage Spaces.

I have 5 x 2 TB of data disks in my server, which are all joined in a Simple space in Storage spaces (for various reasons).

Although, there seems to be no option to replace one of the disks, in my case because I have no space in my server for more HDDs, so I want to change one or two disks to bigger ones.

I blame myself for not reading better about Storage Spaces, but I just assumed it was like a improved version of Windows Drive Extender (where it moved all the data from one disk to the other ones in the pool if you wanted to replace it).

Another scenario could be that I am getting S.M.A.R.T.-varnings about one particular drive and want to replace it, there must be some way to move data from one physical disk and not the whole pool?

Thanks,

Daniel