Move the ULT_Texture_Pack_PT_6_(INSTALL).zip file directly into that folder.
Note: If the filename specifically says "(INSTALL)" and contains another zip inside, you may need to extract it first to find the actual resource pack folder. ULT_Texture_Pack_PT_6_(INSTALL).zip
These packs are extremely hardware-intensive. If your game lags, try lowering your shader settings or allocated more RAM to Minecraft (at least 6-8GB is recommended). Move the ULT_Texture_Pack_PT_6_(INSTALL)
Back in the Minecraft Resource Packs menu, move the pack from the "Available" column to the "Selected" column. ULT_Texture_Pack_PT_6_(INSTALL).zip