"A paragraph is a convenient unit; it serves all forms of literary work. As long as it holds together, a paragraph may be of any length -- a single short sentence or a passage of great duration."
Note the number of sentences in that paragraph by Shrunk and White (2000, p.15), along with their recommendation.
Ah, but some would have one reject all the advice offered by Strunk and White as it is (allegedly) grammatically incorrect. I would not be one of these people, BTW.
OP, if 2 sentences work as a paragraph, I'm not sure why I would "require" a change. However, if the 2 sentences are both rather lengthy, that sounds like a potential problem. Re-writing the long sentences to shorten them with an eye toward clarity will, by default, change the number of sentences in the paragraph (thus taking care of both clarity and perhaps obsolete grammar rules).