Template for 2Dunit100 bmp for SB Red Victory and Others in Series

[Warhorse]

I wanted to modify some unit pictures in the .bmp ,for starters in Red Victory.I tried doing it using cut and paste in XP Paint and had some success but my pictures are slightly out of alignment where the odd picture overlaps other pictures in game.Can I download a gridded empty template so I know exactly where to drop my pasted images?
I would like for example a lightly gridded box that has little spaces to drop all my pictures into the bmp.

A template for Red Victory would be cool,but other games in the series if templates are available I would be interested too.

Alternatively what method is suggested,I am not good with graphics and only want free programs and I sure other paint programs other than old XP Paint would be better.The reason I used XP Paint is because it is really simple interface,I do have WIN 10,but have not used the more modern Win 10 paint,maybe I should or Gimp maybe.
Ideas.

Most paint programs should (I would think) have an option to superimpose a grid on an image. Then, you count the amount of images shown across, divide the pixel count by this and that is the horizontal, then same for height, then you have your centering. Most of the paint programs I used have it, you may have to turn it on first.

To make it easier, here are some of the settings

Info
Units.bmp-108x94
Vehicles.bmp-260x120
Vehicle Wpns.bmp-38x130
Weapons.bmp-38x130
Guns.bmp-260x120
Hvy Weapons.bmp-179x110
Misc.bmp-108x110
Aircraft.bmp-260x120

Map

Guns 100-56x26
Vehicles 100-50x24
2DHvyWpns100-34x20
2DWeapons100-10x34
2D Units100-44x38
3D Vehicles-140x108
2d 100 Misc- 34x34
2d gully100-76x62
2d terrain100-76x62
2d sides 100-76x62

Hope this helps? Oh, try Gimp, it is a free program.