If you want to reduce the weight of your pack, you should do it gradually. Carry less on each trip that you make and for each trip find something that can be replaced with something lighter or left out completely.
If you don’t have enough weight in your backpack, it can be dangerous or uncomfortable. Lightweight backpacking has its own limits. Some of its techniques need to be practiced first. I’m talking here about pitching a tarp properly or choosing the lightweight clothes that will keep you dry and warm. Alcohol stoves also need some practice to use. You should test your skill and learn them better during a short trip or hikes that take only one day. One option at your disposal is going on a hike organized by a company.
First of all, when packing light, buy a scale. Every piece of clothing or gear should be weighed. Write down the weight of each item and some potentially lighter objects that you can use instead. You can see exactly how much weight you save if you get a scale.
Second, pay special attention to the pack, tent and to the sleeping bag. Getting lightweight versions of these items can save you a few pounds. While a lightweight tent has around 4 pounds, a normal one will have 8 or 9. If you go with a bivy or a tarp instead of the tent, it will only weigh around 20 ounces. A backpack that is lightweight will have around 2 pounds, while a regular one will have between 5 and 7. As for the sleeping bag, it usually has around 3 pounds, but a lightweight one will have 19 ounces.
One tip that I have for you is to get the backpack after you bought the other items, so that you know exactly how bit it needs to be to hold everything.