How to up-sample and down-sample a 3D medical image.

I have a 3D volume of the brain and I would like to upsample and downsample in all 3-dimension (x, y and z).

For example, downsample from 170*240*240 => 85*120*120 AND upsample back from 85*120*120 => 170*240*240.

I found this https://www.mathworks.com/matlabcentral/fileexchange/12037-gaussian-pyramid-expand-and-reduce-routines-1d--2d-and-3d on mathswork file-exchange but it is very slow for a 3D-volume. How can I do this efficiently in matlab?