You can re-order your workspace displayed on the far left of your side-menu. There are two possible actions, both using drag&drop.
Move a workspace up or down
You can move a workspace up or down in the side-menu. To do so, simply hover your cursor on the workspace icon, and click to drag it to the desired position. Once the icon is where you want it to be, release your click to drop the icon.
Note that you cannot move a Workspace outside of its subscription represented by the separator lines.
Move a subscription up or down
You workspaces are gathered in subscriptions, so in any case, your workspaces in the same subscription will always be together in the side-menu.
You can move a subscription by hovering your cursor on the small separator above your subscription's workspaces icons. Click and hold to start the drag and drop, then move the subscription where you want, and release to drop it.