For easier opening begin case cover removal with outer corners at back side where connectors and sockets are. Put prying tool in thin gap between cover and bottom plate in one corner and pry cover open. Then do that in opposite side. Continue prying around cover until all cover at front, left and right sides is separated from bottom plate.
In end pry open cover in area between middle antenna connector and blue WAN socket. Be careful though - there is only one thin plastic pin inside. If it doesn’t open easy, do not apply force to it. Cover is now partially open at front side where pin is accessible with long flat screwdriver or other flat metallic tool. Pull pin to your side which will free the cover completely.
Use Opener tool. In absence of it payment card with sharpened edge or disposable plastic knife will work as well. However be careful to avoid breaking plastic pins on inside edges of router case.
Dell Vostro 14 5459 definitely is simple and easy to open. In absence of prying tool you can use even disposable plastic knife. Spent 15 minutes to disassemble, change HDD drive to SSD drive and assemble it back. Memory upgrade is easy as well - carefully peel off plastic sheet above RAM module and replace the RAM. Seems particular cooler design is not very prone to collect dust inside too so easier cleaning as well. If middle screw on assembly doesn’t stick in thread, slightly press keyboard in area where keys G,H,J are and try to screw the screw in again. For maintenance and upgrade for this laptop I give 4/5.
I disassembled and assembled back SM-T805 for motherboard replacement 2 hours ago. Discovered that back cover have a row of tiny pins with tips molded into back cover rim who are designed to break out and larger pins who will click open and back on closing just fine. Also back cover rim is glued to cover with weak glue. Seems someone Samsung decided that those larger pins alone are not enough to keep back cover firmly in place without flapping around. In reality larger pins alone on assembling will click back and keep cover in place just fine.
However I agree to you that correct way is to carefully open this tablet from screen side with these small blue flat openers or with plastic cards. It will be faster as well. Back cover rim should be removed only to replace antennas. I hope that author of these manuals will fix that.