Lag problem

[MiRai]

I tried to lower the resolution.The only problem is that I use the accounts for farming. I need to keep environment detail and view distance high to be able to see far while flying

Just to be clear, video settings do not affect the draw distance of players, NPCs, or anything else you can interact with. If you're using the lowest possible view distance, then it may be difficult to see the node from the absolute furthest distance, but it does not affect the "radar" on your minimap.

I was wondering, if I want to increase the resolution/graphics, I would need to upgrade the GPU ?

You would need to monitor you hardware to know the answer to that.