Thanks Takayuki, I've seen that page but it still doesn't help me. It does not explain in plain language what to do step by step. Also this page talks about Captcha and has to be uploaded to wp/content/uploads but I have Really Simple Captcha which says upload to wp/content/plugins. I just found in my computer files some instructions from a year ago and they worked! This is it:
If you install this manually, follow these steps:
1. Upload the entire really-simple-captcha folder to the /wp-content/plugins/ directory (NOT to the inside of the Contact-Form-7 folder, just loose in plugins).
2. Activate the plugin through the 'Plugins' menu in WordPress.
FYI: There is no "control panel" for this plugin. This means, go to Plugins -> tick the box of the Really Siimple CAPTCHA plugin -> click "Activate"
3. Click Contact-Form-7 Settings -> click Generate Tag (button on the RHS of page) -> click CAPTCHA -> it generates two lines of code in brown boxes. Copy paste them, in the order they appear, into your Contact-Form-7 code over on the left, before the <p>[submit "Send"]</p>
4. Click the Save button.