Tris to Quads
In Edit mode (1), choose Face (2), then Tris to Quads (3). To ensure all faces are selected, push A. This will change triangle polygons to square ones, and reduce complexity.
Decimate is a modifier that simplifies the model’s polygons and complexity in order to reduce the computer’s processing load. This step should be followed by smoothing, beautify and shade smooth.
Switch to Object mode(1). Then click on the wrench to open modifier properties(2).
Select “add modifier” (1) and then “decimate” from the list (2).
Here you can choose the ratio of the decimation. For example .5=50% of the original model complexity.
The polygons have been reduced in this case by half. Finding the perfect mix of reduced polygons and a nice appearance are a matter of experimentation.
To apply the decimation, click first on the arrow next to the decimate modifier.
Click “apply” in the drop-down list to make the decimation permanent.