I have a dual system tablet but I haven’t tried
I allocated more space for my windows(allocating more space for android is different,just for consult)
- make a win8pe udisk then boot to winpe(x86 with uefi support,USB-hdd is ok,It seems that the cpu doesn’t support win7pe)
2.use deskgenius,delete the recovery partition and android partition(delete android will not broke the boot menu,you doesn’t need to delete android)
3.create a new partition or merge the free space,i just creat a new and formated fat32,i don’t know if DG can merge ext3 ,you can try youself
you can use a Windows install udisk to recover you system instead of recovery partition.