In the your Admin Dashboard look for the Fundraising Module and then click on the Donation Pages link. 

Next, locate the page that you would like to edit you type the name of the page in the "search" field or you can sort the Donate Page list by name.

After you locate the page that you want to edit click the "Edit Page" button.

If you want to edit General Information such as name this info can be located on Step 1. Make sure to click the "Save Draft" button after you complete your edits.

Design elements such as donate page copy and colors can be found on Step 2. Make sure to click the "Save Draft" button after you complete your edits.

On "Step 3" you can edit information displayed on the "Thank You" page. This info includes Thank You graphic and message. 

At any time after making an edit simply click the "Save Draft" or "Finish" button.