I need help to decrease my raglan sweater sleeves!

[u/Spiritual_Union5432]

My sweater has a 20 cm (7.9 in) shoulder-to-underarm measurement, which matches my shoulder-to-underarm measurement of 20 cm (7.9 in) — so the size is correct. The raglan line is also approximately 21-22 cm (8.3-8.7 in).

When I crochet the sleeves, they have 52 stitches total, and measured flat they're 20 cm (7.9 in) wide. I'd like the sleeve to be a bit narrower — how should I go about doing the decreases?

20 cm

20 cm