Blocks can be rearranged within your post in a couple of different ways. On the left of each block (or just above the block, if the block is set to display full width), are two block mover arrows (Block Mover Up Arrow Block Mover Down Arrow), and between these arrow icons is a block mover drag handle (Block Mover Drag Handle). These block mover arrows and drag handle will only appear when your cursor is hovering over the block.
Clicking on either of the block mover arrows will move that particular block, further up or down within your page. You can also click and drag on the block mover drag handle, and drag the block up or down the page. When dragging your block, you should see a blue horizontal line appear between the blocks in your page, which indicates where you can drop your block.