Please follow the below steps for sector erase operation.
1. CS# LOW
2. WREN command
3. CS# HIGH
4. CS# LOW
5. Sector erase command (parameter sector or normal sector erase)
6. Address of the sector to be erased
7. CS# HIGH
You can see more details about this in datasheet section "9.6 Erase Flash Array Commands" (page 97, http://www.cypress.com/file/177961/download ).
Thanks and Regards,