Sameh Bayda and his wife Alo-Bridget Namoa, both aged 19, face a maximum penalty of life in prison after their charges were upgraded on Wednesday to conspiring to carry out a stabbing attack in Sydney in late 2015.

The pair have been in custody since they were arrested early last year in Guildford.

At that time, Mr Bayda was charged with three counts of collecting documents likely to facilitate terrorist acts.

He was allegedly found with several Arabic documents outlining how to make an improvised explosive device and carry out a stabbing.

Ms Namoa was charged at the time with recklessly possessing an item connected to a terrorist act and recklessly possessing documents connected to a terrorist act.

It is alleged that police found a knife wrapped in a shahada (Islamic) flag in Ms Namoa's handbag, while she also allegedly sent her husband a text message saying "I want to do an Islamic Bonnie and Clyde on the kaffir".

Mr Bayda is also charged with hindering the investigation by telling his wife to delete messages from her phone and delete material from his phone.

In Central Local Court on Wednesday, prosecutors confirmed that there was no new evidence in the matter.

It is understood that police upgraded the charges after consulting with the Commonwealth Director of Public Prosecutions and receiving advice that the existing evidence could support the more serious charge.

Mr Bayda and Ms Namoa did not appear on screen in court and did not apply for bail.

The police brief of evidence has been completed and the pair are expected to go to a committal hearing when they next appear in court in March.

Ms Namoa is of Tongan heritage and converted to Islam during high school.