For this example we will be replacing the metal plate floor.
1 . Open photoshop and then create a new texture with size 256x256.
2 . Draw whatever you like [you can add some more flowers and rainbow monkeys ... lol just kidding , but you will get nice effect

3 . Now comes the important part. First at the layers palette if you see layers [not only the background], then do this : Right click on a layer's name and then "Flatten Image" ...then Right Click and then Convert to layer.
4 . Now go to Image > Canvas Size and increase it to 512x512. Till the image with 4 layers.
5 . Now flatten the image again.
6 . Go to the chanels pallete and duplicate the blue for example , and name it as Alpha 1, then increase its contrast and brightness for shines , or vice-versa.
7 . Add some tillable detail textures and look which Opacity type suit's your texture the best.
8 . After finished save your texture wherever you like and save it as DXT2\DXT3 if you are editing the Metal Plate floor from b30.
[note : If it says : Too many chanels then right click , then flatten image again.]
9 . Close photoshop and go back to HMT. Click EOF and then hit update.
10 . Import your texture with the larger resolution and when it asks click yes or ok.[note : When using the EOF trick found by Philly the bitmap seperates from the other ones and no bitmap corruption can occur.]
11 . Do not forget about the bump-map. Normalmapfilter your texture and with EOF import them back.
12 . Close HMT and see the floor ingame .
The reason why it happens : "The texture ingame is set to be used larger than the original one , so it increases it's size. Also you might use HCE to increase the size's resizing, and if we increase the size of the texture , ingame it will decrease it's size and will look better."
[note : If you are using this trick I highly recommend you to use it only for the most important bitmaps , or your bitmaps might become +MBs for any map you edit. I edited 7 MP levels and now my bitmaps.map size is 386 MB.]
Also you can resize the detailmaps of one groundmap only in the [senv] tag. A fast tutorial about it. Also Philly found this , and I take no credit for writing it here.
1 . Open bloodgulch for example and go to the [senv] tag.
2 . Go to the blahblahblah\blood ground tag.
3 . Scroll down until you see Primary detailmap scale, scondary map scale, and micro-detailmap scale. Increase them for like : 120 , 130 , 2 and hit save.
4 . Close HMT and see ingame.
The more higher value typed there , the more size-decreased the texture is ingame.
Now go out there and show them some High Quality textures
