No problem at all — this is a completely normal situation for a growing business, and it's solved in just a couple of minutes.
First, check cPanel, in the resource usage statistics section — it will immediately show you exactly which parameter (CPU, RAM, Inodes, or disk space) is approaching its limit. This takes less than a minute.
Then simply go to your Self-Service area and purchase additional resources — exactly as much as you need, nothing more. No lengthy requests, no waiting for support, no need to switch plans — everything is done instantly, on your own.
And here's the best part: you're not locked into this decision forever. If you need less later on, just remove the extra resources you added. The billing period is 1 month, so you're always in full control of your costs and pay exactly for what you use — no overpaying.
Your business grows — and your resources grow right along with it, flexibly and hassle-free.