As your needs change, you might find that your instance is over-utilized (the instance type is too small) or under-utilized (the instance type is too large). If this is the case, you can resize your instance by changing its instance type. For example, if your t2.micro instance is too small for its workload, you can increase its size by changing it to a bigger T2 instance type, such as t2.large. Or you can change it to another instance type, such as m5.large. You might also want to change from a previous generation to a current generation instance type to take advantage of some features, such as support for IPv6.
If you want a recommendation for an instance type that is best able to handle your existing workload, you can use AWS Compute Optimizer.