Your wire or power company's wire? If it is the feeder from the power company, contact them before doing anything. If it is your wire between your buildings, then yes, you need to upgrade the wire to match the service you plan to install. In that case, if you planned ahead and have the old wire in conduit, and the conduit is large enough, pull out the old and pull in the new. If no conduit exists, start digging and install conduit this time and get it right.
If this is a sub-panel feed providing 100A from a main service panel and you want to use a 200A panel as the sub-panel then the answer is no. As long as the feed is protected by a 100A breaker in the main panel it doesn't matter that the sub-panel has a 200A main breaker. Your question is vague.
