In the base, each menu for different things is accessed by talking to the different characters. The upgrades menu is accessed by talking to the second character going left from the main doors. This is a man sitting sharpening a spear with a weapons rack next to him. Pressing 'A' on your controller, or 'X' if using a DS4 enters the upgrades menu.
The first screen shows 3 boxes. The top box is your current weapon, pressing 'A' enters a menu allowing you to select any other weapons you have unlocked. Some weapons are more useful for different levels so you might want to swap between missions.
The second (middle) box shows what item you have currently equipped that provides bonuses.
The third (bottom) box shows what boots you are currently wearing.
You unlock upgrades by completing missions, I can't remember if you have to earn coins to buy each upgrade, been a while since I played it.
Pressing 'A' on each box enters the selection menu.
Weapons Menu, weapons are from top to bottom:
Oak Pole: A basic pole with a red ribbon at one end. Critical hits stun enemies
Forest Rage: A chan dao or monk spade, has a large flat curved blade at one end, a crescent shaped blade at the other. Using Qi restores health.
Fisherman's Pole: A basic bamboo staff. Attack speed increases as the combo counter increases (25% max)
Singed Dragon: Staff with a large curved blade at one end, the inside of the blade has a jagged edge. Typhoon and Rockfall inflict additional fire damage on enemies and surrounding foes
Staff Of Abbott Shuo: Plain wooden shaft with ornate iron shod ends. Casting each seal inflicts 10 points of damage to the enemy. Seal creation +25%
Jade Cliff: Wooden shaft with jade crystal blades at each end. Ghost Aura. Every killed enemy recovers Qi within the aura radius. Ghosts are always corporeal. This is the weapon to use if you're struggling fighting ghosts or spirits.
Jingu Bang: Red and gold staff, each end is shaped like a fist. Increases the strike distance of all staffs by a third
Swamp Claw: A basic spear with red tassels hanging from it. Loaded thrusts poison enemy
Icy Ruin: A navy blue shaft with a curved steel blade at one end. Slows down enemies by 5% per strike (35% max)
Three Steel Widows: A wooden shaft ending in a straight steel blade. Two more blades extend from the blade at 90 degrees to form a cross shape, giving the weapon it's name. Critical hits inflict bleeding.
Items Menu:
18 Arhats: A golden bead necklace. Increases the maximum quantity of Qi by 1.
36 Shaolin Beads: A thick beaded bracelet. Successful parries and received damage regenerate Qi.
108 Passions: A beaded necklace. Passive energy regeneration.
Black Rhino Vambraces: Ornate bracers. Defence + 20%. Additionally, damage is reduced by 20% when attempting to parry powerful attacks.
Boots Menu:
Monk Shoes: Plain yellow shoes. Kick and Gust inflict 20% damage. Dodge inflicts 25% damage.
Sandals Of Nimble Zhe: Plain brown sandals. Increases run and jump speed.
Black Rhino Vambraces: Ornate greaves. Defense + 20%. Dodge, Kick and Burst deflect projectiles.
Golden Putees: Grey boots with golden criss-crossed lacing. Dodge is replaced by Power Dash, which passes through any enemy and bestows invincibility.
Press 'A' to make your selection then go to the bottom of each menu to go back to previous menu showing the 3 items you have equipped, go to the bottom and press 'A' again to save your selection and exit.
Alternatively, once you make your selection pressing 'A' you can exit to previous menu by pressing 'B' and then 'B' again to leave the upgrades menu.