Apple Mac Performa 640 series - Manual (Page 150)

Removing a SIMM
If your computer has a SIMM already installed on the DOS-compatibility
card, follow these steps to remove it.
1 Pull the metal clips at either end of the SIMM away from the SIMM.
Use your fingernails.
2 Rotate the SIMM until it is at a slight angle.
Rotate the SIMM away from its vertical position
to disengage it from the SIMM slot.
To release the SIMM, move the metal clip on each side away from the SIMM.
SIMM slot Vertical plate
142 Appendix B