What is the ideal treatment for a 55-years-female with Simple hyperplasia of the endometrium with Atypia?
Simple hysterectomy
Medroxy progesterone acetate (MPA)
Levonorgesterol (LNG)
IUCD
Management of Atypical Endometrial Hyperplasia:
"Hysterectomy is the best treatment for women at any age with atypical endometrial hyperplasia because the risk of concurrent subclinical invasive disease is high."
Williams Gynae 1st ed p 691
"In presence of atypia, response to progesterone therapy is poor and the relapse rate is high. Nearly one-third of them will progress to cancer and one-fourth may already have associated undiagnosed cancer. In women approaching or post menopause, hysterectomy is a safer choice in those with complex or atypical hyperplasia."  
Jeffcoate 7th/ ed p 425
So Remember: Best management of atypical hyperplasia is hysterectomy.
Also, Know Management of Endometrial Hyperplasia:
Management depends on the patient's age and the presence or absence of cytological atypia.
Non-atypical hyperplasia:

Premenopausal women: Progesterone therapy-

options: - Medroxyprogesterone acetate for 21 days a month daily for 3 months.
Progesterone-containing IUCD.
Postmenopausal women

Simple hyperplasia without atypia - Generally followed without therapy.
Complex hyperplasia without atypia - Cyclical/continuous progesterone therapy.
These patients should be followed annually by endometrial biopsy.


Atypical hyperplasia:

The ideal treatment is a hysterectomy
Premenopausal women willing to preserve fertility - High dose progesterone therapy after full information of risk of undiagnosed cancer or progression to cancer. In these cases periodic TVS and endometrial biopsy is necessary.