Hello,
The M510 AP takes a Micro SIM card and it sounds like you've inserted a 'Nano' sized card.
When the Micro SIM is installed it partially protrudes and it 'clicks' in to place like an SD card, so when pressed in again (to remove), it is pushed out by the mechanism.
If you have inadvertently pushed in a Nano sized SIM then I'm not sure how you will remove it.
You can download the M510 Quick Start Guide document with the details here:
https://support.ruckuswireless.com/documents/2353-ruckus-m510-access-point-quick-setup-guideGood luck,
Darrel.