You can use the inline editor by logging in:
Then click on the edit tool, then click enable.
At this point you can edit your content live as shown here:
When finished, click on save and then disable your editor to keep from making unwanted edits.
Another way is to use the global editor function.
Do this by logging in, then clicking on edit above the content.
This will bring up this editor:
To insert an image, choose a location for an image, then click on this button:
You will be able to upload a new image by using this button:
This will allow you to browse for an image, or drag one on the window. Then click on upload.
Then click on the image and choose insert.
Once you’ve inserted the image, you can resize it by using the handles.