Picture Posting/Pixel Size Tech Question

I'm trying to post a picture to a thread. I keep getting this: "The Dimension limits for this filetype are 800 x 800. We were unable to resize your file so you will need to do so manually and upload it again. Your file is currently 3456 x 2304". I went into photoshop and I can resize the image, but how can I resize the pixels? Resizing the image didn't help the pixel size. Thanks!

One way (PS7): Go to (menu) Image> Image Size
Be sure that the box for Constrain proportions is checked.
Be sure that "Resample Image" is Bicubic.
Change "Resolution" to 72
Change the biggest of "Pixel Dimensions" to 800.

IMAGE POSTING RULES
If you're going to "Attach" it, the file size must be below 100KB.

Many thanks, you're beautiful!

BTW, sharpen after you resize.