Hi pookiefeb
Unfortunately there isn't a merge function we could use here.
You could probably achieve this through customization but I get the feeling it would be more effort than needed for what is probably only an occassional occurrence.
What you could do is create an activity under the lead you want to keep and use it to summarise the previous contact with the other lead. If there were only a handful of activities you could even add each one individually.
I hope that helps.
Jeff