How to easily resize pics for this forum

This picture was originally taken with a resloution of 4000 x 2672 pixels. The size of this file is 6.54MB. (Five 3-1/2" floppies for us older guys lol). If I attempt to upload this picture, the forum will tell me it is too large, therefore I must resize it. Of course, I would hate to resize the original picture, because then when I go to view it or print it later, it would not have enough detail to prevent it from looking fuzzy.

First, I will resize it so that the horizontal size goes from 4000 pixels to 640 pixels.

The resulting picture ends up with a resloution of 640 x 428 pixels. File size is now 70.8KB (1000KB = 1MB). Considerably smaller.