How do I redefine a named range with VBA?

I have a named range called "X" which is 1000 rows and I want to dynamically reduce this to 100.

I tried Range("X").Resize(100,1) and also .Resize(-900,0) but neither seem to change the size of the named range when I check in excel by selecting the range from the range drop-down menu. What am I doing wrong?