Upgrading from Shimano Altus

[Stefx73]

Hi

I have an iGo Quindici E-Comodo e-bike.
The crank has one speed (42T) and the rear derailleur/shifter is Shimano Altus with a Shimano ACSHG2007232 7-speed cassette.
On my road bike I have Shimano 105, and on my Hybrid I have Shimano Deore. I really miss the feeling of crips precise shifting.

I want to upgrade the Altus components to a better quality combination.
I assume I have to upgrade the cassette, rear derailleur, shifter and chain?
Will the crank also have to be upgraded or can I just replace the current ring on the current crank?

Any advice would be appreciated.
Thanks

 

[FlatSix911]

Here is the Shimano Hierarchy for Road and Mountain groupsets.

If you like your 105 Road, I would recommend Deore or SLX for smoother shifting.