After I imported from blogger, the images from old posts are the wrong size.

I successfully imported my old posts from blogger to wordpress. The posts are mostly pictures, and now that they are in wordpress, they are all the wrong size. Do I have to manually go through and change each old posts picture size so that they look right with my new wordpress theme? Please tell me it is easier than this. I am not skilled with coding, and am VERY new to all of this. HELP!