What are you trying to accomplish?
If you just want more horizontal space for your Watch List page, you may be able to use an ad blocker's element hiding utility to hide the menu items on the left side of the page, making your Watch List items span the entire page.
The links that appear at the left side of the Watch List page are also available by hovering your cursor over the My eBay link in the upper right of the page.
If you have an ad blocker installed in your browser, such as AdBlock or Ad Block Plus, you can use that to block various page elements. Most common browser will let you install such add-ons. If you do not have an ad blocker yet, google those names and the first result should have a link to let you install it in your browser. There are other ad blockers such as uBlock Origin.
Using AdBlock, choose "hide something on this page" then hover the cursor over the part of the page you want to block.
Ad Block Plus has a similar feature called "Block element" that also lets you block page features using a point an click interface.
If you block the wrong thing, you can turn of ad blocking on that page or site, or edit your filter rules to undo the block and try again.
