how to upgrade Elasticache Redis clusters from 6.2.6 to 7.0.5

Hello,

We have one application using ElastiCache Redis cluster 6.2.6 and we would like to upgrade to 7.0.5 so that the automatic updates happen after that. What is the process to do the upgrade? How can we make sure the key values do not get lost during the upgrade? Also how to enable encryption at rest and in transit? Please let us know. Thanks in advance.