Another nice AutoCAD express tool I use is the GATTE tool. Or better known as the Global attribute editor. This command will change values for all insertions of a specific block in your drawing. Then will allow you to specify a new value for one of the attributes & automatically replaces all values with the same tag name. Whats nice about this tool is if your attributes values are different you can still update them all to one value. With FIND/REPLACE you would need to run a find for each different type of value to replace with your new one.
To start the command, type in GATTE on your command line. This will issue the Global attribute edit command. Next you will be prompted to select your attribute or block to edit. Once you directly select the attribute annotation value you want to edit it will prompt you for a new value. Next specify your new attribute values, hit enter, and confirm to process the attributes. If you don't want to update EVERY block you can say NO when prompted to process them all, and select only the block instances you want to process.
Here is some screen captures of the steps.
Now it will tell you how many attributes will be updated. Hit yes to process them all.
And here is the final result with all your attributes with that same TAG name updated.