You have three virtual machines (VM1, VM2, VM3) in an availability set named AVSet1. You need to resize VM1 to a new VM size, but the desired size is not available. What should you do first?

To resize a virtual machine to a size that is not currently available, you must first deallocate the VM. Deallocating a VM releases the compute resources (CPU, memory) it was using, allowing Azure to reallocate it to different hardware that supports the desired VM size. Simply stopping or shutting down a VM (without deallocating) retains its allocated resources, preventing a resize to an unavailable size. Creating a proximity placement group is for latency optimization, not resizing. Converting to a managed availability set is irrelevant to the immediate task of resizing.