To upload background images on Taobao PC, you can follow the steps below:

1. Open Taobao Seller Center: Log in to Taobao Seller Center URL (https://myseller.taobao.com/), enter your Taobao account and password to log in.

2. Enter the store management backend: After logging in to the seller center, click the "Shop Management" button at the top of the page to enter the store management backend.

3. Select store decoration: In the store management backend, find the "Shop Decoration" option on the left menu bar and click to enter.

4. Enter page editing mode: On the store decoration page, click the "Page Edit" button at the top to enter page editing mode.

5. Add background image: In page editing mode, find the "Page Settings" option on the left menu bar and click to enter.

6. Select background image: On the page settings page, you can choose to upload a new background image or use an existing background image. If you choose to upload a new picture, please click the "Upload" button and select the image file you want to upload.

7. Adjust the image size and position: On the page settings page, you can adjust the size and position of the background image to meet your aesthetic needs.

8. Save and preview: After completing the setting of the background image, click the "Save" button to save your changes. Then, click the "Preview" button to view the store page and make sure that the background image is displayed correctly.

9. Publish the store: Finally, click the "Publish" button to publish your store page. Now, your Taobao PC store should have successfully set the new background image.

Note: If you are not familiar with page editing operations, you can refer to Taobao's official documentation or consult professionals. At the same time, in order to maintain the beauty and user experience of the store page, it is recommended to choose a high-quality, appropriately sized background image.