My dear, whatever may happen never refer to yourself as ' ugly'.
Beauty is a perception... and its not always external.... !
Dark color of your arms and legs could be due to harmful effects of Sun.
First and foremost always apply sunscreen.
The right method of application is that apply liberally, 10 - 15 min before steppin out into the sun and re apply after 2-3 hours.
A broad spectrum sunscreen such as 'Suncross aquagel' will be good and non sticky for a tropical climate.
For lightening you can try creams such as 'Kojivit' but considering it is a large body part it is usually not convinent to apply creams.
You can opt for Chemical peels
such as Glycolic or TCA
peels, for which your cosmetologist can guide you.
At home you can try a mix of gram flour(besan) with milk, apply like a paste keep for 5 min and wash it off, you can do this 2-3 times a week and follow it with a moisturizing lotion.
Let me know the progress.