Terjemahan:Abang saya mau mengganti bajunya.
Abang means 'older brother'. Although the person might not actually BE your brother. And they might not be older. If your boyfriend is one year older than you, you can still call him 'abang' In some areas 'kakak' has the same meaning, but 'older sister', but in some just 'older sibling'.
Adik means 'younger sibling'.
Saudara means 'sibling'.
In practice 'saudara laki-laki saya' is not something people really say. Probably you would say:
"abang saya" or "abangku" "adik saya" or "adikku" (which is not gender-specific, but whereas in English you would always say "my brother" or "my sister" when referring to a specific person, and very rarely "my sibling", in Indonesian it's MUCH more usual to just say "adik" and leave out the gender.
So the natural translation is one of "abang saya", "abangku", "adik saya" or "adikku".