How can I change the instance type of my nodegroup?

From the point of view of eksctl, nodegroups are immutable. This means that once created the only thing eksctl can do is scale the nodegroup up or down.

To change the instance type, create a new nodegroup with the desired instance type, then drain it so that the workloads move to the new one. After that step is complete you can delete the old nodegroup.

How do I set up ingress with eksctl?

If the plan is to use AWS ALB Ingress controller, setting nodegroups[*].iam.withAddonPolicies.albIngress to true will add the required IAM policies to your nodes allowing the controller to provision load balancers. Then you can follow https://kubernetes-sigs.github.io/aws-alb-ingress-controller/guide/controller/setup/.

For Nginx Ingress Controller, setup would be the same as any other Kubernetes cluster (see (https://kubernetes.github.io/ingress-nginx/deploy/#aws)[https://kubernetes.github.io/ingress-nginx/deploy/#aws]).