I would suggest that you loosen the bottom screw first but do not remove it. Then loosen both the top screws, remove the bottom screw and finally remove the top screws.
For assembly, install and start the bottom screw but do not tighten it. Install and start the top screws, taking them down almost to where they start to tighten. Finish the bottom screw and then finish the top screws.
The above is not critical but makes it easier. Using the right screwdriver, however, is essential. You will find that purchasing a good gunsmith's set of hollow ground screwdrivers or driver and bit set is well worth the investment.