Acer Aspire E1-521 Service Manual page 144

Remove the two (2) screws securing the mainboard to the lower case.
5.
Pull the mainboard by the right side to release the connectors from the slots on the lower case.
6.
5-45
Figure 5:62. Removing the Mainboard Screws
Figure 5:63. Removing the Mainboard
Service and Maintenance