it would be amazing if the players could update BP, example: they start with 3 lines and can update for some raw materials + 3 fields or 1 lines and so up to a maximum of 7 lines. Of course, the number of raw materials for the update would also increase, the material for the update could be set in the config, It would be amazing, thanks

Such an upgrade feature could easily be realized in an independant plugin which grants the different permissions.
I might work on something like that, however it's hard for me to dedicate more time to uMod lately so alternatively you could request such a plugin in the plugin requests section.

We use GUIShop and sell an upgrade by adding the user to a group.  This group has permissions for the larger backpack.

You could use PlayerRankings plugin (by Ankawi) which is time on server related and grant the permissions for backpacks plugin when a certain amount of time (=rank which you created) has been reached, I use this method for kits and other rewards.
it might be not exactly be what you want but usually the more time a player stays on the server the more they have gathered.

thank you for the answer, I already have everything, but it would be great to add a function to update the backpack, the player gives the command example: / backpack update and if he has the necessary resources so the backpack will need to expand 3 slots, to the maximum