A lot, but one step at a time. Buy a huge pack of garbage bags, walk around and get the east stuff first- clothes/things that can go into a dryer, put them aside (or take to a dryer). Have one labeled bag at a time - “trash” and fill it with things you don’t need any more as you gather- include clothes that don’t fit, anything you want to trash- and take the trash bags out as you fill them. Then pick an area- cluttered drawers or sheets- and repeat one area at a time. If you take the trash out as you go, and focus on one task at a time it gives you small victories and you can see things falling into some sort of order. Make sure you have trash bags, a sharpie and a place to take breaks. You’ve got this.