Just wanted to share my experience of downloading the TOPO Great Britain v2 PRO 1:25K maps to me new Garmin Edge 1030 Plus in case anyone else has the same problems I encountered (I have now solved the problem).
The Garmin website says that 3.3 GB are required for these maps (which include the full Ordnance Survey 1:25 maps of GB). I had just the Cycle Maps of Europe installed and according to Garmin Express and windows explorer I had 14 GB of free space on the device. However, when I tried to install the maps I got a message that there was insufficient memory.
I was advised by cutsomer support to remove the Cycle Maps of Europe and then install the TOPO maps (although they couldn't explain why this would be necessary if I had 14 GB of free space). I followed the advice and the TOPO maps installed successfully. However, far form requiring 3.3 GB, the maps were actually 5 files totalling something like 15 GB. So now I didn't have room to reinstall the Cycle Maps of Europe.
Fortunately I discovered from elsewhere on this forum that there were map files on the device for North Africa (2.9 GB) although these don't show in Garmin Express. As I am unlikely to go cycling in North Africa any time soon I made a copy of this file on my PC and deleted it from my device. I then had sufficient room to reinstall the Cycle Maps of Europe. Although I was told by Support that I wouldn't be able to reinstall the North Africa map due to copyright protection I have successfully swapped around the Africa maps. I think the copyright protection just prevents installation on another device to the one originally installed on.
I also recommend installing Basecamp to help when reviewing the the maps installed on your device. Garmin Express does not recognise all the maps, but Basecamp will show all maps installed and give you details of the file name etc.
Garmin Support have told me that they have asked for the website to be updated to correct the space required for the TOPO maps but in the meantime, if you can't download the maps, this may be the cause!