Hello @Aya Elmir,
In your post above you mention being given a link, but you did not supply it here. If in fact your university directed you to the IBM SPSS Statistics Subscription Trial, then indeed you would have a 30 days of "trial" and your next step forward would be to purchase a subscription for the needed time period.
Alternatively, if your university already has an ongoing license/subscription, then you would need to work with them to get yourself added as a validated user on their agreement with IBM SPSS.
Here is main page for the IBM SPSS Statistics product, detailing the various options for purchase
------------------------------
David Dwyer
SPSS Technical Support
IBM Software
------------------------------