It is permissible for the pilgrim performing Umrah to shorten his hair and he does not have to shave it. It is recommended for him to shave his hair or shorten it at Al-Marwah
وَحَدَّثَنَا حَجَّاجُ بْنُ الشَّاعِرِ، حَدَّثَنَا مُعَلَّى بْنُ أَسَدٍ، حَدَّثَنَا وُهَيْبُ بْنُ خَالِدٍ، عَنْ دَاوُدَ، عَنْ أَبِي نَضْرَةَ، عَنْ جَابِرٍ، وَعَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، - رضى الله عنهما - قَالاَ قَدِمْنَا مَعَ النَّبِيِّ صلى الله عليه وسلم وَنَحْنُ نَصْرُخُ بِالْحَجِّ صُرَاخًا .
jibir and Abil Salld al-Khudri (Allah be pleased with them) reported: We went with Allah's Messenger (ﷺ) and we were pronouncing Talbiya for Hajj loudly.