First, quick clarification: when you say "two slots are being used," I’m assuming you mean ARC Pro subscription seats (PC activations). If you actually mean the Connection skill’s EZ-B connection slots, tell me and I’ll give those steps instead.

If you mean ARC Pro seats, here’s how to free up a seat on your main PC so the LattePanda can take it.

Steps - release the seat from the main PC

1. In ARC on the main PC, open the Help tab click Manage Subscription.
   • This opens your subscription portal. (You can also open the portal directly at: https://synthiam.com/Account/Subscription)
2. Sign in with the account that owns the subscription.
3. In the subscription portal you will see a list of assigned seats (computer names).
   • Locate the main PC entry that is currently consuming a seat.
4. Click the Revoke / Release Seat Token button for that computer to free its seat.
   • The seat is immediately released and becomes available to activate on another machine (your LattePanda).

Activate the LattePanda

1. On the LattePanda, open ARC. When prompted to activate a seat, press Activate.
   • If not prompted, open Help Manage Subscription inside ARC and follow the activation flow. See: https://synthiam.com/Support/Install/subscription-plans/assign-seat
2. The LattePanda will consume the freed seat and show in the portal as an assigned computer.

Other options (if you don’t want to revoke)

• If you want the main PC to keep ARC but not use a seat, you can remove activation on that machine the same way (revoke), then sign into ARC on the main PC with a non-Pro account or run the free version.
• You can add associated accounts (Account Subscription Add Associated Account) so other users can use subscription seats without sharing credentials: https://synthiam.com/Support/Install/subscription-plans/manage-subscription

If you’re actually referring to EZB Connection slots (the Connection control showing two EZB indexes in use), tell me:

• whether you want to disconnect one EZ-B (which frees that EZB index), or
• if you want to use the LattePanda as a headless ARC install while still keeping the main PC connected.

I can walk you step-by-step (with screenshots if you want) - which slot type are you referring to (subscription seat vs. EZB connection index)?