LTSPICE IV - How to...
How to change logic levels in LTSPice?
Right-mouse-click on the device in your schematic.
A dialog will be shown.
Enter the parameter(s) into any of the fields
from "Value" to "SpiceLine2".
Vhigh=5 Vlow=0 Ref=1.5
Trise=5n Tfall=5n Td=5n
"Ref" is the threshold. Default is (Vhigh+Vlow)/2
Don't connect anything to unused inputs!