1. If zipped, unzip all downloaded Landsat scenes. 
2. Copy all TIF files into a temporary folder such as the Desktop. This makes the import easier and the files can be deleted afterwards.
3. Start SAGA GIS. If you do not have a copy, download it from here.
4. From the main menu, select Geoprocessing -> File -> Grid -> Import -> Import, Clip and Resample Grid to open this tool, as shown below.

SAGA Clip and Resample Tool

6. Within this window set the options as:
   • Image Files >>                 Select the raw, unzipped imagery downloaded from the USGS website  (all files exept BQA) – see an example below.
   • User Defined No-Data Value >> tick box
   • No-Data Value >>          0 (default)
   • Resample >>                    tick box
   • Cell Size >>                      100
   • Region of Interest >>     Select the ROI file created previously in Step 3b

Select files for all bands. BQA indicates Quality assessment and is not needed. B1 and B9 contain cloud information and thus are less relevant. So is the panchromatic band B8.

Move back to the Overview Move to Step 5