Dave is right about making the correction under Admin > Club Setup > Club Names, Logos, Dues and Points. However, this will not automatically change any existing Fee records. You will need to open each Fee record and typeover the Amount to change it from $26 to $28, tab out of the Amount field, then Save And Close.
Or AFTER RUNNING THE BACKUP UTILITY:
you could run an SQL statement like:
update Fee set Amount = 28 where Amount = 26 and Club_Year = '2011-2012' and For_Dues=True
this will mess up the Balance Due on each affected Fee record though, so you will have to run the OPTIMIZE procedure (under Admin > Database Utilities) and select the Checkbox to "Recalculate the Balance Due on all Fees"
Just to be safe... do a screen print of the main Ledger > Fees grid BEFORE you try this. Then, when you're done, compare the results with the screen print to be sure the results are exactly what you expected.