How can I concat multiplexed fastq files from two lanes?

Hi there! I just got some reduced-genome sequencing (GBS) data of a population, including 150 samples. I used two lanes to generate data form the same population, then I got two bid multiplexed fastq files. I want to concat the fastq of each sample, not merge the two files head to tail, i.e. eventually 150 rows in total. Can I concat the two big files without demultiplexing them into single fastq?

Thank you.