Wiktionary
vb. 1 (context intransitive English) to wash or groom oneself in order to be more attractive 2 (context transitive English) to freshen, make fresh, revivify, make new.
WordNet
Usage examples of "freshen up".
I went in to freshen up, and all I could think was I was going to have amazing sex with this perfect man.
She needed to freshen up more than she needed to worry about her modesty.
Afterward I was exhausted, and the orgy I had started was going strong, but some of the girls and guys went for a swim to freshen up and cool off, and there I ran into my companion, Norman.
I don't know about you, but I'm going out to do a little shopping, and then freshen up for dinner.
Time to use the washroom, freshen up, have breakfast, and take a cab to the center of London’.