It look a bit small on screen but hopefully it will give you an idea. The main steps are: click >options before opening the file just to confirm your settings. Unfortunately, there are no hard and fast rules about the options to set in here and on more complex files it will invovlve trial and error. Then click >open. RMB on the composite in the browser and click >copy to construction environment. Drag the End Of Part marker above the composite feature. RMB on the EOP marker and click>delete all features below marker. RMB on the construction folder and click >edit construction. Expand out the folder to see what it contains. RMB on the surfaces node and click >unstitch. RMB on the surfaces node and click>quality check>examine. It passes - good news! RMB on the surfaces node and click >stitch. Notice it stitches up cleanly into a solid. Now RMB on the solid and >copy object. Select solid to copy the new solid from the Construction Environment to the part environment. RMB and click>exit construction environment. You're back in the usual part editing environment. RMB on the construction folder and click >delete. Pat yourself on the back as you've translated your first iges file!
JD - I'm sure there might be some comments or feedback but I think I've covered most of it?