replacing my user account

A Genius at the Apple store recommended that I create a new primary user account and dump the old one, in order to escape a lot of general slowness that is limited to my primary user account. He didn't tell me exactly how to do this. My question is how to make sure the new user has access to all my documents, music, photos, and applications, while leaving behind whatever corrupted software is slowing my computer.

Can Migration Assistant do this?

The slowness is especially noticeable when searching—in Finder, in Spotlight, and especially in Mail. I've tried making Spotlight stop indexing and then re-index, several times. The computer can get sluggish in many Finder functions as well.

OS X 10.9.5

Mini 2.5 GHz Intel Core i5 8GB/500 GB (290 free)

External hard drive 500 GB (150 free)