You can write your Japanese name, Sachiko in three ways; Hiragana, Katakana and Kanji.
Hiragana and Katakana are phonetic script, so さちこ for Hiragana, サチコ for Katakana.
There are many variations of Kanji on Sachiko; 幸子 佐知子 佐智子 紗智子 .....
Therefore, if you want to know which you should write, 幸子 or サチコ, the answer is both ^-^