Aura instances come predefined with resources allocated for memory (RAM), storage (disk) and processing capacity (CPU) and have been carefully tuned and configured to perform well.
If you find that you may need more memory or more CPU or storage to meet the needs of your application workload then you will need to align the resource need to the standard offering.
AuraDB Professional does not allow for customisation of resources.
See the full instance sizes details here: https://aura.support.neo4j.com/hc/en-us/articles/360053015393-What-are-the-Aura-instance-sizes-available-per-subscription-tier-Professional-Enterprise-
Pricing details: https://neo4j.com/cloud/aura/pricing/