If this doesn't do the trick there is an accessory called a handlebar riser. Costs $6 from an overseas seller Bicycle Fork Stem Extender Bike Handlebar Riser Head Up Adapter Aluminium Alloy | eBay or $8 from a US source Bicycle Fork Stem Extender Bike Handlebar Riser Head Up Adapter Aluminium F6N2 | eBay
The one you find in most bike shops is made by Delta and costs about $20. I used this one on my mountain bike when I wanted to bring the handlebars up and closer to me. https://www.amazon.com/Delta-Alloy-B.../dp/B000FHBED0

The one you have on the bike requires using two metric hex wrenches to loosen it. I tried doing it on an older bike with one of these and couldn't budge the bolt. Some previous owner or bike shop had really horsed down on it when they tightened it.