Is changing straight hair to slightly curly hair considered a lack of contentment, or dissatisfaction, or altering Allah's creation, or is it a normal matter?

If the purpose of curling hair is for adornment, and it does not involve imitating disbelievers or transgressors, and you are sure that no harm will result from it, then there is no objection to it. The basic principle is that there is no harm in curling the hair of the head, and this applies to both men and women alike. This is not considered altering Allah's creation or a blameworthy dissatisfaction, unless it involves discontent.