بسم الله الرحمن الرحيم
If you do not have amount sufficient for performing hajj, but you have sufficient amount to perform umrah then it is correct to perform umrah without doubt. Hajj shall be fardh when you will have the capacity to perform hajj. It is better to perform umrah during days other than the months of Hajj (i.e. 1st Shawwal to 10th Dhul Hijjah).
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.