I have migrated everything over from my 12 year old iMac to my new MacBook Air.

I think I may have made a huge mistake. I’ve bought a MacBook Air and used the migration tool to transfer EVERYTHING over from my 12 year old iMac to my new MacBook Air. I think I’ve probably used up all of the MacBook air’s memory and clogged it up with loads of stuff I don’t need. I thought I was doing the right thing.

Can I reverse this and start again fresh on my new MacBook Air