There are a couple of ways to find synonyms in Word 2013.
To go straight to the thesaurus, click Review > Thesaurus.
The Thesaurus list opens with a list of synonyms for any selected word.
To insert or copy a word from the Thesaurus, pause over the word so you can click the dropdown arrow, and then click Insert or Copy. To keep looking, click any word in the Thesaurus list to switch to synonyms for that word.
The other way to find synonyms is to simply right-click any word in your document and click Synonyms. This opens a short list.
If you see a word you like, click it to replace the original word.
If none of the words is quite right, click Thesaurus at the bottom of the list to see more possibilities.
More about finding the right words
To see how else the thesaurus can help you, check out the table in Find synonyms with the thesaurus.