[purl4peace]

Next Row[RS] K1, k2tog, k to last 3 sts, sL1K, k1, psso, k1.

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Working all raglan armhole decrease as set by ast row, dec 1st at each end of 4th [4th, 4th, 2nd, 2nd, 2nd] and ever foll alt row until 43 [45, 47, 47, 53, 55] sts rem.
Work 1 row, ending with RS facing for next row.

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I need help in understanding the lines that I have marked within the red lines. Please help.[/QUOTE]

Here's my take:

1. There is a typo which I believe should be "as set by LAST row" (perhaps you typed that part in wrong"... last row referring to:

Next Row[RS] K1, k2tog, k to last 3 sts, sL1K, k1, psso, k1.

2. The "ever foll alt row" also looks funky but I interpret that as "every following (as in "successive") alternating row".

In other words, if you are working one of the first 3 sizes, after your first decrease as specified by:
Next Row[RS] K1, k2tog, k to last 3 sts, sL1K, k1, psso, k1.

your next set of decreases will come after you have worked 4 rows... then every other row after that (keeping in mind that you have to decrease from both sides regardless of whether it is after working 4 rows or 2)

If you are working in one of the last 3 sizes, then you'll just work your decrease every other row until you get down to the right number of stitches.

Not sure if that helps. (Raglan sleeves are why I usually stick to drop shoulders ;-)