Yes mate, open your photo in a good image editing program like Adobe Photoshop, click on > Image > Image Size or Edit and you should see a box with some numbers pop up. Put in the values you want, to reduce the size of the image (width/height), make sure you keep the same dimensions (constrain proportions) first.
As your computer screen can only display 72 dpi (dots per inch), if your resolution is greater than 72 reduce the dpi to 72, this will reduce the picture size. Mostly higher dpi are used for printing where you will want 200-300 dpi to produce more detail in a printed photo. But for computers, firstly reduce the dpi, then constrain the proportions and reduce either width or height.
This will also reduce the physical file size as well so you wont have to upload too many kbs to the Cr0 server. There is actually a file size limit but im not sure what it is.
Hope this helps
Ashes