Correct me if I am wrong but were you not able to upload once you had resized the files? That is the only way to upload files directly (size/dimensions should be within the upload limits).
2) How do I know if my Upload & Sell membership is activated and what are the size/dimension
restrictions?
Your service is active when you see "Upload & Sell: On" on your profile.
In order to make the forum experience enjoyable to all members including those on dial-up,
we allow files up to 550kb in size. There are no restrictions on image dimension, but please
keep files around 800px, so that members using monitors with lower resolution can also
enjoy viewing your photos.
prasanna,
Actually you can go even bigger than that. (Up to 650kb). That is a huge image size for web presentation. Once you resize your full sizes images and jpeg compressed them, images should average around 350kb.
All the best,
Fred