S3 Browser allows you to easily determine what storage class is used for a particular file.
When you browse an S3 Bucket, all files and folders are displayed in the Files table. The 5th column shows what Storage Class is used for an each file. This information is returned with bucket listing, so no extra API calls are required.

File's Storage Class is displayed in the 5th column of the Files table.
Storage Class is also displayed in files' properties on Properties Tab.

File Properties. Reduced Redundancy Storage is used for an file s3browser-2-3-1.exe
Currently Amazon S3 provides two storage options: STANDARD and REDUCED_REDUNDANCY.
If you are storing your file with STANDARD storage option, Amazon S3 guarantes 99.999999999% durability and to sustain the concurrent loss of data in two facilities. If you are using REDUCED_REDUNDANCY, you may expect 99.99% durability and to sustain the loss of data in a single facility.
Why you may want to use Reduced Redundancy Storage? Pricing for Amazon S3 Reduced Redundancy Storage starts at only $0.10 per gigabyte per month and decreases as you store more data. So, you may want to reduce your costs by storing non-critical, reproducible data at lower levels of redundancy than the standard storage of Amazon S3
With S3 Browser you can also easily switch to Reduced Redundancy Storage. Storage class can be changed for one or multiple files as well as for a whole bucket. Check out step-by-step instructions below to learn how.
To edit Storage Class for one or multiple files
Select the file(s) you want to change storage class for and right-click on them. The following menu will appear: 
Select one or multiple files and right-click on them to show context menu.
Choose Change Storage Class.. -> REDUCED_REDUNDANCY or STANDARD correspondingly.
If you will change Storage Class for a folder(s) as decribed above, S3 Browser will enumerate all objects inside the folder and will apply new Storage Class for an each file.
If you need to apply Reduced Redundancy Storage for all files inside the bucket, you need to go through the steps very similar to described above. - Select the bucket.
- From context menu choose Change Storage Class.. -> REDUCED_REDUNDANCY or STANDARD.

Right-click on the bucket and choose desired storage class.
- S3 Browser will apply selected storage class for all files inside the bucket.
If your Amazon S3 Bucket contains a lot of files, this operation may take a while. You can significantly increase performance using S3 Browser Pro. It allows you to increase the number of concurrent working threads and thereby process your files much more faster.