How does Lowry show that Jonas is changed by the memories he receives?
It is Chapter Seventeen that you would benefit from examining in order to respond to this question. This chapter details the day of leisure that the community is given and also the game that Jonas witnesses Asher and his friends playing. What Jonas realises, however, is that the game they are playing is based on war, which is something that he has received the memory of and so understands intimately. He therefore finds himself cut off from his former friends and unable to take pleasure in the kind of activities and diversions that he used to enjoy with them. Note what the narrator tells us as Jonas sits by himself:
Jonas trudged to the bench beside the Storehouse and sat down, overwhelmed with feelings of loss. His childhood, his friendships, his carefree sense of security--all of these things seemed to be slipping away. With his new heightened feelings, he was overwhelmed by sadness at the way the others had laughed and shouted, playing at war. But he knew that they could not understand why, without the memories.
The knowledge that Jonas is given because of the memories that he receives is something that profoundly separates him from his community and makes him isolated. His understanding can actually be seen therefore as more of a curse than a blessing. Lowry displays this through focusing on the feelings of Jonas as he struggles to accept his new position and role in his community.