Left and right nibble from unsigned

Hello guys im new here so pardon me if i made some mistakes in making 
this post.

I'm doing my assignment and I need to find left and right nibble of 
unsigned signal.

signal wdata:unsigned (7 down to 0);
This is the signal from i need to take left and right nibble.So how 
should i do it should i declare two unsigned signals with 4 bits and 
trie to slice the wdata or something else.Thank you in advance.