First question - do the funds you own basically meet the category of investments you want (i.e., if these funds are holding US large, small, Int'l large, small in about the proportions you want)?
If the answer is yes, then you should wait to sell them until they have long term capital gains - the differential in tax costs will outweigh the expense ratio by a lot.
If the answer is no, then the question becomes more complicated but boils down to- what is it worth to you to meet your desired allocation? If you have mostly stock and want to move to mostly bond, then some selling probably makes sense. In most cases, though, if the stock/bond ratio of your holdings is approximately what you want to end up with, it makes sense to wait until you can exchange at the long-term rate. (Hey - by then, it may even be losses if the market tanks - even more valuable