I downloaded and burnt windows 8.1 from MSDN, but during installation I noticed that when I formatted and deleted particular partitions they won't merge into one as in windows 7 installation (as far as I remember). I had 4 partitions: 50GB 200GB 175GB and 30GB, when I deleted 50 and 30 parts they still stayed as partitions which didn't merge. I want to divide mentioned partitions into 40 GB parts. Extend option was disabled. What did I do wrong ?
The GUI for Windows Setup is known to be a little goofy, it`s kinda designed to be "easy" to use, but if you know what you're doing its better to use the command prompt to manage the disks with diskpart commands.
Press Shift + F10 during the install to get a command prompt.
EXTEND THE PARTITION TO FREESPACE
ONLY DO THIS IF YOU DONT WANT DATA ON THE DISK
If you don't want any of the data on the local system, just go nuclear, make it easy, clean and wipe the whole disk.
For more info on using DiskPart from the commandline: