Can I knit a 2 ply Latvian mitten pattern in 4 ply?

I have a book of lovely Latvian mittens, but they are all for 2 ply, which I find is just too thin. Can i knit them in 4 ply? Will it change the size? Do I need to change the stitch numbers?

Help please!

First I would print a scan or copy of the pattern.
Next knit a swatch to get the gauge using the 4 ply yarn.
Now you can calculate which pattern size you need to follow.
For example if the 2 ply yarn gauge is 32 stitches to 4"/10cm
a 7" palm would need 32/4=8x7=56sts approx.
If the 4 ply yarn gauge is 28 stitches to 4"/10cm
a 7" palm would need 28/4=7x7=49sts approx.
Follow the pattern size that uses closest to 49sts approx. and your mitten should fit. Apply the same calculation to check the length gauge if the pattern does specify the number of inches/cm to work.
Also consider a thicker yarn will make a thicker fabric that might make the mitten uncomfortable - just a thought. You might be happier sticking with the 2 ply yarn.