it’s a very basic way, but I will just be disclosing the work flow that makes it more efficient and fast, because it can be needed in many situations and modifiers like Decimate and Remesh doesn’t always cut it in such situations.
so
- select the object
- go into edit mode
- pick edge select
- select all the vertical edges between two loops on any part of your mesh (you can use the Ctrl + shift + Numpad + after you have selected 2 edges)
- go to the select menu
- pick checker deselect.
Make sure the ratio of the “selected” to the “deselected” are 1:1.
Confirm that the middle line of your object is not selected by adjusting the “offset”. - go to the select menu again
- pick select loops from the menu
- then select edge loops from the select loops sub-menu
- now just press right click and dissolve edges
Now just do the same for horizontal edge loops if needed
it’s a very handy way if you want to decrease the faces on certain areas without affecting the others or if you just want to tone down the number of faces on the whole mesh while preserving detail and circulation of the mesh.
if you need a video version check it here