There are 3 modulation schemes are used in lte .
2. 16 QAM
3. 64 QAM
Based on the Channel Quality Indicaiton reported by UEs to eNB. Enodeb MAC scheduler chooses appropriate modulation scheme to send data. As usual if radio conditions are good scheduler would like to send more data(more bits over the one resource element) so it will use 64 QAM. Similarly for other two. I am just telling about PDSCH which is mainly used for data so modulation schemes varies. But some channels like PDCCH and PBCH are in LTE system which mainly focus on reliable delivery of control data UE/UEs,so QPSK is used to send control information.