You are approaching the limit on the number of attachments you can have on a board.

[Danielle]

I've had this warning come up: 

You are approaching the limit on the number of attachments you can have on a board. Please remove any attachments which are unnecessary.

What's the best way to view old archived cards and delete those? They will be years old at this point. 

[Aaron Pavez _ServiceRocket_]

Hi @Danielle 

Here is a good approach mentioned by the Atlassian team:

https://community.atlassian.com/forums/Trello-questions/Re-Limit-on-the-number-of-attachments-allowed-on-a-trell/qaq-p/2336222/comment-id/76429#M76429

The best thing to do to stop you hitting the limit on attachments on this board will be to move cards to another board, there are a couple of ways you could do this:

Regards - Aaron

[Danielle]

Thank you, it's a good approach for future/new cards but doesn't help me with viewing/deleting archieved cards to make the space

[Gaurav Kataria]

If you copy the board, then the new board will have all your active cards (but will not copy over the archived cards), which should automatically free up the space.