First i downloaded node version v10.13.0, now i need to use older version 8.11.3 so i downgraded the node version referencing to this answer. After succesful installation, i modified the PATH  as they suggest by adding 
C:\Users\Administrator\AppData\Roaming\nvm\v8.11.3
to System Variable. I also find out that i have 3 copy of this path 
C:\Program Files\nodejs
in my System Variable(one i've added by myself when i downloaded first time the v10.13.0-version and the rest 2 have no idea how got there, not sure if it is useful to metion here). After all these i switched to older version and tried to check the node version, then the window pops out with error message C:\Program Files\nodejs\node.exe Node.exe is not a valid 32-bit application and the below console output. No related info out there, who could help me out with that ? And by the way,isn't that message should appear if you run 64-bit application on 32-bit OS ? That is weird, because i'm using Win7 64-bit OS.
C:\Users\Administrator>node -v
v10.13.0
C:\Users\Administrator>npm -v
6.4.1
C:\Users\Administrator>nvm ls
  * 10.13.0 (Currently using 64-bit executable)
    8.11.3
C:\Users\Administrator>nvm use 8.11.3
Now using node v8.11.3 (64-bit)
C:\Users\Administrator>node -v
access denied.
C:\Users\Administrator>npm -v
access denied.
access denied.
C:\Users\Administrator>nvm ls
10.13.0
8.11.3
C:\Users\Administrator>nvm -v
Running version 1.1.7.
 
    