Please use [code][/code]
tags around your code and data, to preserve formatting and to improve readability. Please do not use quote tags, colors, or other fancy formatting.
col1 col2 col3 col4 col5
With proper code tags we can now see that the columns are tab-delimited, with most fields being empty. It seems that each line only has two fields, whatever the column number?
Your description says "merge column 2 and 5", but your example shows a merging of column 1 with whatever the second column is. So what is it exactly?
In any case, there are many possible solutions, but assuming the example, one possibility is with sed
sed -r '1d ; s/([^[:blank:]]+)[[:blank:]]+([^[:blank:]]+).*/\1\t\2/' file.txt
" deletes the first line, then the second regex extracts two blank-delimited strings from the line and combines them into the final output.
Here are a few useful sed references.
Please clarify your requirements further if this doesn't satisfy you.