It is known that in tamattu`, one of the three types of Hajj, the pilgrim enters into ihram for `Umrah, then goes out of ihram when he finishes the rituals of `Umrah and enjoys everything that was prohibited to him during ihram. Then he enters into ihram again for Hajj and takes it off when he finishes it.
The late Sheikh Ibn `Uthaymeen, a prominent Saudi Muslim scholar (may Allah shower mercy on his soul), stated the following: If the person who is doing tamattu` enters ihram, then he decides, after performing the `Umrah and before he enters ihram for Hajj, not to perform Hajj, then he does not have to do anything, unless he had made a vow. If he made a vow to perform Hajj this year then he has to fulfill his vow, but if he did not make a vow then there is no blame on him if he does not perform Hajj after doing `Umrah.