Start with a winnowing of the gear that never gets used on trips.
Did you bring anything on this last trip that didn't get used, or only got used because you brought it? If so, try going without on the next trip. Don't count your first aid kit among this gear, though.
Next, you've already taken a look at your sleeping gear and backpack. Great! However, don't rush out and make a purchase just yet.
Start by looking at lightweight options for your shelter. What kind of weather do you usually face on trips? Are there lots of bugs? Would you be happy with a tarp tent set-up, a pair of hammocks, or even something so minimalist as a tarp and a pair of bivvies? That'll start you looking in the right direction for the conditions expected on the majority of your trips. For me, since I live in Florida, an hammock (to keep me off of the ground, away from the bugs and the swamp water) was a good call: it doesn't get cold for the majority of the year, so the "cold backside" problems that others face are actually a plus in the sweltering heat.
Next, look at lightweight options for your insulation. Here, you need to make the call on whether you want one sleep system for all of the weather you may encounter or if you want multiple systems geared to the summer, shoulder seasons, and winter. Summer trips (depending on location) can be really lightweight, while deep winter means more weight. Are you willing to use a pad and a top quilt rather than a full bag? You can shed weight that way. Or do you want the draft blocking capabilities of a full mummy bag? You can avoid carrying extra clothes that way.
Next, take a look at your clothing system. What sort of temperatures are you looking at for your trips? For warm weather (above 50 F at night), I don't carry extra clothing except for a set of fresh undies (helps with hygene issues in hot weather). For colder trips (40 F to freezing), I carry a longsleeve baselayer, a pair of socks, and a wool cap for sleeping in. For colder trips (down to 20 F), I add a fleece and a pair of long underwear rather than the regular compression short undies. My top quilt doubles as a puffy layer, so I've also got that for colder temps in the morning around camp.
Next, look at your rain gear. This is an essential part of your clothing system and temperature management system. It can be a windbreaker layer for when the temperatures are lower, allowing you to leave a dedicated wind shirt home. How light is it, and how much rain protection are you getting from it? Personally, I like a poncho since it vents better than most jackets and doubles as a pack cover (eliminating that weight from my pack). However, again, I hike in warmer weather than most of the country.
Next, look at your miscellaneous stuff. Is there a lighter way to treat your water? Is there a lighter stove option out there for you? Are your ditty bag items (headlamp, firestarter, knife, etc.) heavier than they need to be? Etc.
Finally, and only last, should you be looking at a new pack. Once you've got the rest of your gear dialed in, you can choose the right pack for it. That way, you know what weight you're going to be carrying most of the time and what volume it's going to take up. This allows you to decide on how burly a pack you need and how large it needs to be.
Hope it helps!