Someone has access?

Though I know my way around windows apps and os quite easily, i’ve never really studied tcp/ip, i mean someone keeps hacking (deleting or changing passwords) to my accounts. I would be so very gratefull for any info on how to find out who it is (tho i;m sure i know) but how do you go about getting them back, nothing malicious, just to let them know via email even, that i know what they are upto?