The I-Ride Trolley Red Line has a stop near the Hilton GVC.
You have two choices: Get off the Red Line at Universal Blvd and I-Drive and walk across the bridge to CityWalk, or...
Switch to the Green Line (free transfer, ask the driver) and take it to Major Blvd and walk from there to CityWalk.
Going to Major Blvd gets you a wee bit closer, but my guess is that the total time would be about the same with either option. Either way, it's a longish walk.
Note: I-Ride Trolley stops running at 10:30 pm, so you might need to get a taxi back.