How To Change The Size Of The RDS Instance
The size of the RDS instance can be scaled horizontally or vertically based on the requirements.
Based on the usage of the RDS instance by the application we can downgrade the RDS instance size for saving cost or we can increase the size of the RDS DB instance for the better application performances.
But downgrading the RDS instance size will result in downtime , hence it is recommended to perform such actions during non-production hours , Also Multi-AZ is highly recommended.
In this guide , We will learn how to upgrade and downgrade the size of the RDS DB Instances.
Also , Its highly recommended to maintain a backup (snapshot) of the RDS instances.
Upgrade The Size Of RDS Instance
To upgrade the size of the RDS instance , Login to RDS console.
In the navigation pane.Choose Databases

Select the database you wish to upgrade , For this tutorial , We are going to upgrade an RDS instance from db.t2.micro to db.t2.medium

and then click Modify.

You will see the modify DB instance Page.
As you can see , Currently the RDS instance is running with db.t2.micro instance class.

From the drop down menu , You can find the lists of available RDS instance types.

For this tutorial , Lets upgrade the RDS instance from db.t2.micro (1 VPC , 1 GiB RAM) to db.t2.medium (2 VCPU , 4 GiB RAM).
From the drop down menu , Choose db.t2.medium.

Scroll down and then click Continue
Choose Apply Immediately , For the changes to take effect immediately.

and then click Modify DB Instance.
The Status of the RDS instance will change from Available to Modifying

Once the changes are applied , The RDS DB instance becomes Available and Its ready to accept connections from the Applications.
Downgrade The Size Of RDS Instance
Depending on the performance and usage of the RDS instances by the applications , We may end up in reducing the size of the RDS instance in order to save some money , Instead of simply letting it run.
From the previous steps , We have seen how we can upgrade the RDS instance size.
But this example helps us to downgrade the size of the RDS DB instances.
Make sure We always maintain a snapshot (backup) of the RDS instances for Point In time recovery due to any errors.
Lets Login to RDS console and then choose the Databases.
Select the RDS DB instance which you want to downgrade and the click Modify.
Lets say , For this tutorial , We are going to downgrade the size of the RDS instance from db.t2.medium to db.t2.micro.
From the Modify DB Instance page
Change the DB Instance class from db.t2.medium to db.t2.micro.

and then Scroll down and click Continue
Choose Apply Immediately , To apply the changes right away.
and then click Modify DB Instance
The Status of the RDS instance will change from Available to Modifying
Once the changes are applied , Then the RDS instance will be Available
Now the RDS instance is able to receive connections from the users and the applications.
Conclusion
We have learnt how to successfully upgrade and downgrade the size of the RDS instances.
Hope you find it helpful. Please do check out my other publications.