The magic African knots make these bracelets very adjustable like very few other bracelets or bangles of any design. In the two knot versions, both knots slide. So slide them open before you put it on, then slide them closed to your comfort level once it is on your arm. The knots may be stiff at first on new ones. This is good since then they will stay tight longer. It works best if you can slide both knots at the same time and rate, though this is not necessary.
Another trick (especially if you are alone) is to put your hand firmly on a cloth covered table, so it holds at least one of the knots, while you gentle slide the other knot. Do each one a little distance at a time and it will be nicely balanced when you are done.
For 3 knot bracelets, the middle knot is decorative only, so do not use or move it as part of putting on the bracelet. Of course, once it is on, you can position the third knot wherever you like, if it is able to slide.
For 4 knot bracelets, all 4 knots slide. But notice how they are grouped in pairs – with each member of a pair being at the ends of an area where there are overlapping strands. Treat each of these pairs just like a 2 knot bracelet above.
In all cases, adjust for comfort once it is on. Feel free to bend the main strands slightly to form your preferred shape around your wrist as very few of us actually have round arms – more like oval often.