Checking the resolution

Today i uploaded the pictures i had got from home from my memory stick the the computer, i then loaded the picture into photoshop and realised that my picture did not have the correct resolutions, therefore i needed to get the original picture to ensure that the resolution hasn't been changed whilst being uploaded onto the computer. I went into image and clicked on image size and it showed me that the resolutio was not high enough, however when i changed it to 200 it went fuzzy. I then changed my picture to CMYK and saved it to my area and back to my memory stick. I also changed my image to TIFF instead of JPG.